// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/fs/exec.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

/*
 * #!-checking implemented by tytso.
 */
/*
 * Demand-loading implemented 01.12.91 - no need to read anything but
 * the header into memory. The inode of the executable is put into
 * "current->executable", and page faults do the actual loading. Clean.
 *
 * Once more I can proudly say that linux stood up to being changed: it
 * was less than 2 hours work to get demand-loading completely implemented.
 *
 * Demand loading changed July 1993 by Eric Youngdale.   Use mmap instead,
 * current->executable is only used by the procfs.  This allows a dispatch
 * table to check for several different types  of binary formats.  We keep
 * trying until we recognize the file or we run out of supported binary
 * formats.
 */

#include <linux/kernel_read_file.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/mm.h>
#include <linux/stat.h>
#include <linux/fcntl.h>
#include <linux/swap.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/sched/mm.h>
#include <linux/sched/coredump.h>
#include <linux/sched/signal.h>
#include <linux/sched/numa_balancing.h>
#include <linux/sched/task.h>
#include <linux/pagemap.h>
#include <linux/perf_event.h>
#include <linux/highmem.h>
#include <linux/spinlock.h>
#include <linux/key.h>
#include <linux/personality.h>
#include <linux/binfmts.h>
#include <linux/utsname.h>
#include <linux/pid_namespace.h>
#include <linux/module.h>
#include <linux/namei.h>
#include <linux/mount.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/tsacct_kern.h>
#include <linux/cn_proc.h>
#include <linux/audit.h>
#include <linux/kmod.h>
#include <linux/fsnotify.h>
#include <linux/fs_struct.h>
#include <linux/oom.h>
#include <linux/compat.h>
#include <linux/vmalloc.h>
#include <linux/io_uring.h>
#include <linux/syscall_user_dispatch.h>
#include <linux/coredump.h>
#include <linux/time_namespace.h>
#include <linux/user_events.h>

#include <linux/uaccess.h>
#include <asm/mmu_context.h>
#include <asm/tlb.h>

#include <trace/events/task.h>
#include "internal.h"

#include <trace/events/sched.h>

static int bprm_creds_from_file(struct linux_binprm *bprm);

int suid_dumpable = 0;

static LIST_HEAD(formats);
static DEFINE_RWLOCK(binfmt_lock);

void __register_binfmt(struct linux_binfmt * fmt, int insert)
{
        write_lock(&binfmt_lock);
        insert ? list_add(&fmt->lh, &formats) :
                 list_add_tail(&fmt->lh, &formats);
        write_unlock(&binfmt_lock);
}

EXPORT_SYMBOL(__register_binfmt);

void unregister_binfmt(struct linux_binfmt * fmt)
{
        write_lock(&binfmt_lock);
        list_del(&fmt->lh);
        write_unlock(&binfmt_lock);
}

EXPORT_SYMBOL(unregister_binfmt);

static inline void put_binfmt(struct linux_binfmt * fmt)
{
        module_put(fmt->module);
}

bool path_noexec(const struct path *path)
{
        return (path->mnt->mnt_flags & MNT_NOEXEC) ||
               (path->mnt->mnt_sb->s_iflags & SB_I_NOEXEC);
}

#ifdef CONFIG_USELIB
/*
 * Note that a shared library must be both readable and executable due to
 * security reasons.
 *
 * Also note that we take the address to load from the file itself.
 */
SYSCALL_DEFINE1(uselib, const char __user *, library)
{
        struct linux_binfmt *fmt;
        struct file *file;
        struct filename *tmp = getname(library);
        int error = PTR_ERR(tmp);
        static const struct open_flags uselib_flags = {
                .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
                .acc_mode = MAY_READ | MAY_EXEC,
                .intent = LOOKUP_OPEN,
                .lookup_flags = LOOKUP_FOLLOW,
        };

        if (IS_ERR(tmp))
                goto out;

        file = do_filp_open(AT_FDCWD, tmp, &uselib_flags);
        putname(tmp);
        error = PTR_ERR(file);
        if (IS_ERR(file))
                goto out;

        /*
         * may_open() has already checked for this, so it should be
         * impossible to trip now. But we need to be extra cautious
         * and check again at the very end too.
         */
        error = -EACCES;
        if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) ||
                         path_noexec(&file->f_path)))
                goto exit;

        error = -ENOEXEC;

        read_lock(&binfmt_lock);
        list_for_each_entry(fmt, &formats, lh) {
                if (!fmt->load_shlib)
                        continue;
                if (!try_module_get(fmt->module))
                        continue;
                read_unlock(&binfmt_lock);
                error = fmt->load_shlib(file);
                read_lock(&binfmt_lock);
                put_binfmt(fmt);
                if (error != -ENOEXEC)
                        break;
        }
        read_unlock(&binfmt_lock);
exit:
        fput(file);
out:
        return error;
}
#endif /* #ifdef CONFIG_USELIB */

#ifdef CONFIG_MMU
/*
 * The nascent bprm->mm is not visible until exec_mmap() but it can
 * use a lot of memory, account these pages in current->mm temporary
 * for oom_badness()->get_mm_rss(). Once exec succeeds or fails, we
 * change the counter back via acct_arg_size(0).
 */
static void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
{
        struct mm_struct *mm = current->mm;
        long diff = (long)(pages - bprm->vma_pages);

        if (!mm || !diff)
                return;

        bprm->vma_pages = pages;
        add_mm_counter(mm, MM_ANONPAGES, diff);
}

static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
                int write)
{
        struct page *page;
        struct vm_area_struct *vma = bprm->vma;
        struct mm_struct *mm = bprm->mm;
        int ret;

        /*
         * Avoid relying on expanding the stack down in GUP (which
         * does not work for STACK_GROWSUP anyway), and just do it
         * by hand ahead of time.
         */
        if (write && pos < vma->vm_start) {
                mmap_write_lock(mm);
                ret = expand_downwards(vma, pos);
                if (unlikely(ret < 0)) {
                        mmap_write_unlock(mm);
                        return NULL;
                }
                mmap_write_downgrade(mm);
        } else
                mmap_read_lock(mm);

        /*
         * We are doing an exec().  'current' is the process
         * doing the exec and 'mm' is the new process's mm.
         */
        ret = get_user_pages_remote(mm, pos, 1,
                        write ? FOLL_WRITE : 0,
                        &page, NULL);
        mmap_read_unlock(mm);
        if (ret <= 0)
                return NULL;

        if (write)
                acct_arg_size(bprm, vma_pages(vma));

        return page;
}

static void put_arg_page(struct page *page)
{
        put_page(page);
}

static void free_arg_pages(struct linux_binprm *bprm)
{
}

static void flush_arg_page(struct linux_binprm *bprm, unsigned long pos,
                struct page *page)
{
        flush_cache_page(bprm->vma, pos, page_to_pfn(page));
}

static int __bprm_mm_init(struct linux_binprm *bprm)
{
        int err;
        struct vm_area_struct *vma = NULL;
        struct mm_struct *mm = bprm->mm;

        bprm->vma = vma = vm_area_alloc(mm);
        if (!vma)
                return -ENOMEM;
        vma_set_anonymous(vma);

        if (mmap_write_lock_killable(mm)) {
                err = -EINTR;
                goto err_free;
        }

        /*
         * Place the stack at the largest stack address the architecture
         * supports. Later, we'll move this to an appropriate place. We don't
         * use STACK_TOP because that can depend on attributes which aren't
         * configured yet.
         */
        BUILD_BUG_ON(VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP);
        vma->vm_end = STACK_TOP_MAX;
        vma->vm_start = vma->vm_end - PAGE_SIZE;
        vm_flags_init(vma, VM_SOFTDIRTY | VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP);
        vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);

        err = insert_vm_struct(mm, vma);
        if (err)
                goto err;

        mm->stack_vm = mm->total_vm = 1;
        mmap_write_unlock(mm);
        bprm->p = vma->vm_end - sizeof(void *);
        return 0;
err:
        mmap_write_unlock(mm);
err_free:
        bprm->vma = NULL;
        vm_area_free(vma);
        return err;
}

static bool valid_arg_len(struct linux_binprm *bprm, long len)
{
        return len <= MAX_ARG_STRLEN;
}

#else

static inline void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
{
}

static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
                int write)
{
        struct page *page;

        page = bprm->page[pos / PAGE_SIZE];
        if (!page && write) {
                page = alloc_page(GFP_HIGHUSER|__GFP_ZERO);
                if (!page)
                        return NULL;
                bprm->page[pos / PAGE_SIZE] = page;
        }

        return page;
}

static void put_arg_page(struct page *page)
{
}

static void free_arg_page(struct linux_binprm *bprm, int i)
{
        if (bprm->page[i]) {
                __free_page(bprm->page[i]);
                bprm->page[i] = NULL;
        }
}

static void free_arg_pages(struct linux_binprm *bprm)
{
        int i;

        for (i = 0; i < MAX_ARG_PAGES; i++)
                free_arg_page(bprm, i);
}

static void flush_arg_page(struct linux_binprm *bprm, unsigned long pos,
                struct page *page)
{
}

static int __bprm_mm_init(struct linux_binprm *bprm)
{
        bprm->p = PAGE_SIZE * MAX_ARG_PAGES - sizeof(void *);
        return 0;
}

static bool valid_arg_len(struct linux_binprm *bprm, long len)
{
        return len <= bprm->p;
}

#endif /* CONFIG_MMU */

/*
 * Create a new mm_struct and populate it with a temporary stack
 * vm_area_struct.  We don't have enough context at this point to set the stack
 * flags, permissions, and offset, so we use temporary values.  We'll update
 * them later in setup_arg_pages().
 */
static int bprm_mm_init(struct linux_binprm *bprm)
{
        int err;
        struct mm_struct *mm = NULL;

        bprm->mm = mm = mm_alloc();
        err = -ENOMEM;
        if (!mm)
                goto err;

        /* Save current stack limit for all calculations made during exec. */
        task_lock(current->group_leader);
        bprm->rlim_stack = current->signal->rlim[RLIMIT_STACK];
        task_unlock(current->group_leader);

        err = __bprm_mm_init(bprm);
        if (err)
                goto err;

        return 0;

err:
        if (mm) {
                bprm->mm = NULL;
                mmdrop(mm);
        }

        return err;
}

struct user_arg_ptr {
#ifdef CONFIG_COMPAT
        bool is_compat;
#endif
        union {
                const char __user *const __user *native;
#ifdef CONFIG_COMPAT
                const compat_uptr_t __user *compat;
#endif
        } ptr;
};

static const char __user *get_user_arg_ptr(struct user_arg_ptr argv, int nr)
{
        const char __user *native;

#ifdef CONFIG_COMPAT
        if (unlikely(argv.is_compat)) {
                compat_uptr_t compat;

                if (get_user(compat, argv.ptr.compat + nr))
                        return ERR_PTR(-EFAULT);

                return compat_ptr(compat);
        }
#endif

        if (get_user(native, argv.ptr.native + nr))
                return ERR_PTR(-EFAULT);

        return native;
}

/*
 * count() counts the number of strings in array ARGV.
 */
static int count(struct user_arg_ptr argv, int max)
{
        int i = 0;

        if (argv.ptr.native != NULL) {
                for (;;) {
                        const char __user *p = get_user_arg_ptr(argv, i);

                        if (!p)
                                break;

                        if (IS_ERR(p))
                                return -EFAULT;

                        if (i >= max)
                                return -E2BIG;
                        ++i;

                        if (fatal_signal_pending(current))
                                return -ERESTARTNOHAND;
                        cond_resched();
                }
        }
        return i;
}

static int count_strings_kernel(const char *const *argv)
{
        int i;

        if (!argv)
                return 0;

        for (i = 0; argv[i]; ++i) {
                if (i >= MAX_ARG_STRINGS)
                        return -E2BIG;
                if (fatal_signal_pending(current))
                        return -ERESTARTNOHAND;
                cond_resched();
        }
        return i;
}

static int bprm_stack_limits(struct linux_binprm *bprm)
{
        unsigned long limit, ptr_size;

        /*
         * Limit to 1/4 of the max stack size or 3/4 of _STK_LIM
         * (whichever is smaller) for the argv+env strings.
         * This ensures that:
         *  - the remaining binfmt code will not run out of stack space,
         *  - the program will have a reasonable amount of stack left
         *    to work from.
         */
        limit = _STK_LIM / 4 * 3;
        limit = min(limit, bprm->rlim_stack.rlim_cur / 4);
        /*
         * We've historically supported up to 32 pages (ARG_MAX)
         * of argument strings even with small stacks
         */
        limit = max_t(unsigned long, limit, ARG_MAX);
        /*
         * We must account for the size of all the argv and envp pointers to
         * the argv and envp strings, since they will also take up space in
         * the stack. They aren't stored until much later when we can't
         * signal to the parent that the child has run out of stack space.
         * Instead, calculate it here so it's possible to fail gracefully.
         *
         * In the case of argc = 0, make sure there is space for adding a
         * empty string (which will bump argc to 1), to ensure confused
         * userspace programs don't start processing from argv[1], thinking
         * argc can never be 0, to keep them from walking envp by accident.
         * See do_execveat_common().
         */
        ptr_size = (max(bprm->argc, 1) + bprm->envc) * sizeof(void *);
        if (limit <= ptr_size)
                return -E2BIG;
        limit -= ptr_size;

        bprm->argmin = bprm->p - limit;
        return 0;
}

/*
 * 'copy_strings()' copies argument/environment strings from the old
 * processes's memory to the new process's stack.  The call to get_user_pages()
 * ensures the destination page is created and not swapped out.
 */
static int copy_strings(int argc, struct user_arg_ptr argv,
                        struct linux_binprm *bprm)
{
        struct page *kmapped_page = NULL;
        char *kaddr = NULL;
        unsigned long kpos = 0;
        int ret;

        while (argc-- > 0) {
                const char __user *str;
                int len;
                unsigned long pos;

                ret = -EFAULT;
                str = get_user_arg_ptr(argv, argc);
                if (IS_ERR(str))
                        goto out;

                len = strnlen_user(str, MAX_ARG_STRLEN);
                if (!len)
                        goto out;

                ret = -E2BIG;
                if (!valid_arg_len(bprm, len))
                        goto out;

                /* We're going to work our way backwards. */
                pos = bprm->p;
                str += len;
                bprm->p -= len;
#ifdef CONFIG_MMU
                if (bprm->p < bprm->argmin)
                        goto out;
#endif

                while (len > 0) {
                        int offset, bytes_to_copy;

                        if (fatal_signal_pending(current)) {
                                ret = -ERESTARTNOHAND;
                                goto out;
                        }
                        cond_resched();

                        offset = pos % PAGE_SIZE;
                        if (offset == 0)
                                offset = PAGE_SIZE;

                        bytes_to_copy = offset;
                        if (bytes_to_copy > len)
                                bytes_to_copy = len;

                        offset -= bytes_to_copy;
                        pos -= bytes_to_copy;
                        str -= bytes_to_copy;
                        len -= bytes_to_copy;

                        if (!kmapped_page || kpos != (pos & PAGE_MASK)) {
                                struct page *page;

                                page = get_arg_page(bprm, pos, 1);
                                if (!page) {
                                        ret = -E2BIG;
                                        goto out;
                                }

                                if (kmapped_page) {
                                        flush_dcache_page(kmapped_page);
                                        kunmap_local(kaddr);
                                        put_arg_page(kmapped_page);
                                }
                                kmapped_page = page;
                                kaddr = kmap_local_page(kmapped_page);
                                kpos = pos & PAGE_MASK;
                                flush_arg_page(bprm, kpos, kmapped_page);
                        }
                        if (copy_from_user(kaddr+offset, str, bytes_to_copy)) {
                                ret = -EFAULT;
                                goto out;
                        }
                }
        }
        ret = 0;
out:
        if (kmapped_page) {
                flush_dcache_page(kmapped_page);
                kunmap_local(kaddr);
                put_arg_page(kmapped_page);
        }
        return ret;
}

/*
 * Copy and argument/environment string from the kernel to the processes stack.
 */
int copy_string_kernel(const char *arg, struct linux_binprm *bprm)
{
        int len = strnlen(arg, MAX_ARG_STRLEN) + 1 /* terminating NUL */;
        unsigned long pos = bprm->p;

        if (len == 0)
                return -EFAULT;
        if (!valid_arg_len(bprm, len))
                return -E2BIG;

        /* We're going to work our way backwards. */
        arg += len;
        bprm->p -= len;
        if (IS_ENABLED(CONFIG_MMU) && bprm->p < bprm->argmin)
                return -E2BIG;

        while (len > 0) {
                unsigned int bytes_to_copy = min_t(unsigned int, len,
                                min_not_zero(offset_in_page(pos), PAGE_SIZE));
                struct page *page;

                pos -= bytes_to_copy;
                arg -= bytes_to_copy;
                len -= bytes_to_copy;

                page = get_arg_page(bprm, pos, 1);
                if (!page)
                        return -E2BIG;
                flush_arg_page(bprm, pos & PAGE_MASK, page);
                memcpy_to_page(page, offset_in_page(pos), arg, bytes_to_copy);
                put_arg_page(page);
        }

        return 0;
}
EXPORT_SYMBOL(copy_string_kernel);

static int copy_strings_kernel(int argc, const char *const *argv,
                               struct linux_binprm *bprm)
{
        while (argc-- > 0) {
                int ret = copy_string_kernel(argv[argc], bprm);
                if (ret < 0)
                        return ret;
                if (fatal_signal_pending(current))
                        return -ERESTARTNOHAND;
                cond_resched();
        }
        return 0;
}

#ifdef CONFIG_MMU

/*
 * During bprm_mm_init(), we create a temporary stack at STACK_TOP_MAX.  Once
 * the binfmt code determines where the new stack should reside, we shift it to
 * its final location.  The process proceeds as follows:
 *
 * 1) Use shift to calculate the new vma endpoints.
 * 2) Extend vma to cover both the old and new ranges.  This ensures the
 *    arguments passed to subsequent functions are consistent.
 * 3) Move vma's page tables to the new range.
 * 4) Free up any cleared pgd range.
 * 5) Shrink the vma to cover only the new range.
 */
static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
{
        struct mm_struct *mm = vma->vm_mm;
        unsigned long old_start = vma->vm_start;
        unsigned long old_end = vma->vm_end;
        unsigned long length = old_end - old_start;
        unsigned long new_start = old_start - shift;
        unsigned long new_end = old_end - shift;
        VMA_ITERATOR(vmi, mm, new_start);
        struct vm_area_struct *next;
        struct mmu_gather tlb;

        BUG_ON(new_start > new_end);

        /*
         * ensure there are no vmas between where we want to go
         * and where we are
         */
        if (vma != vma_next(&vmi))
                return -EFAULT;

        vma_iter_prev_range(&vmi);
        /*
         * cover the whole range: [new_start, old_end)
         */
        if (vma_expand(&vmi, vma, new_start, old_end, vma->vm_pgoff, NULL))
                return -ENOMEM;

        /*
         * move the page tables downwards, on failure we rely on
         * process cleanup to remove whatever mess we made.
         */
        if (length != move_page_tables(vma, old_start,
                                       vma, new_start, length, false, true))
                return -ENOMEM;

        lru_add_drain();
        tlb_gather_mmu(&tlb, mm);
        next = vma_next(&vmi);
        if (new_end > old_start) {
                /*
                 * when the old and new regions overlap clear from new_end.
                 */
                free_pgd_range(&tlb, new_end, old_end, new_end,
                        next ? next->vm_start : USER_PGTABLES_CEILING);
        } else {
                /*
                 * otherwise, clean from old_start; this is done to not touch
                 * the address space in [new_end, old_start) some architectures
                 * have constraints on va-space that make this illegal (IA64) -
                 * for the others its just a little faster.
                 */
                free_pgd_range(&tlb, old_start, old_end, new_end,
                        next ? next->vm_start : USER_PGTABLES_CEILING);
        }
        tlb_finish_mmu(&tlb);

        vma_prev(&vmi);
        /* Shrink the vma to just the new range */
        return vma_shrink(&vmi, vma, new_start, new_end, vma->vm_pgoff);
}

/*
 * Finalizes the stack vm_area_struct. The flags and permissions are updated,
 * the stack is optionally relocated, and some extra space is added.
 */
int setup_arg_pages(struct linux_binprm *bprm,
                    unsigned long stack_top,
                    int executable_stack)
{
        unsigned long ret;
        unsigned long stack_shift;
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma = bprm->vma;
        struct vm_area_struct *prev = NULL;
        unsigned long vm_flags;
        unsigned long stack_base;
        unsigned long stack_size;
        unsigned long stack_expand;
        unsigned long rlim_stack;
        struct mmu_gather tlb;
        struct vma_iterator vmi;

#ifdef CONFIG_STACK_GROWSUP
        /* Limit stack size */
        stack_base = bprm->rlim_stack.rlim_max;

        stack_base = calc_max_stack_size(stack_base);

        /* Add space for stack randomization. */
        stack_base += (STACK_RND_MASK << PAGE_SHIFT);

        /* Make sure we didn't let the argument array grow too large. */
        if (vma->vm_end - vma->vm_start > stack_base)
                return -ENOMEM;

        stack_base = PAGE_ALIGN(stack_top - stack_base);

        stack_shift = vma->vm_start - stack_base;
        mm->arg_start = bprm->p - stack_shift;
        bprm->p = vma->vm_end - stack_shift;
#else
        stack_top = arch_align_stack(stack_top);
        stack_top = PAGE_ALIGN(stack_top);

        if (unlikely(stack_top < mmap_min_addr) ||
            unlikely(vma->vm_end - vma->vm_start >= stack_top - mmap_min_addr))
                return -ENOMEM;

        stack_shift = vma->vm_end - stack_top;

        bprm->p -= stack_shift;
        mm->arg_start = bprm->p;
#endif

        if (bprm->loader)
                bprm->loader -= stack_shift;
        bprm->exec -= stack_shift;

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        vm_flags = VM_STACK_FLAGS;

        /*
         * Adjust stack execute permissions; explicitly enable for
         * EXSTACK_ENABLE_X, disable for EXSTACK_DISABLE_X and leave alone
         * (arch default) otherwise.
         */
        if (unlikely(executable_stack == EXSTACK_ENABLE_X))
                vm_flags |= VM_EXEC;
        else if (executable_stack == EXSTACK_DISABLE_X)
                vm_flags &= ~VM_EXEC;
        vm_flags |= mm->def_flags;
        vm_flags |= VM_STACK_INCOMPLETE_SETUP;

        vma_iter_init(&vmi, mm, vma->vm_start);

        tlb_gather_mmu(&tlb, mm);
        ret = mprotect_fixup(&vmi, &tlb, vma, &prev, vma->vm_start, vma->vm_end,
                        vm_flags);
        tlb_finish_mmu(&tlb);

        if (ret)
                goto out_unlock;
        BUG_ON(prev != vma);

        if (unlikely(vm_flags & VM_EXEC)) {
                pr_warn_once("process '%pD4' started with executable stack\n",
                             bprm->file);
        }

        /* Move stack pages down in memory. */
        if (stack_shift) {
                ret = shift_arg_pages(vma, stack_shift);
                if (ret)
                        goto out_unlock;
        }

        /* mprotect_fixup is overkill to remove the temporary stack flags */
        vm_flags_clear(vma, VM_STACK_INCOMPLETE_SETUP);

        stack_expand = 131072UL; /* randomly 32*4k (or 2*64k) pages */
        stack_size = vma->vm_end - vma->vm_start;
        /*
         * Align this down to a page boundary as expand_stack
         * will align it up.
         */
        rlim_stack = bprm->rlim_stack.rlim_cur & PAGE_MASK;

        stack_expand = min(rlim_stack, stack_size + stack_expand);

#ifdef CONFIG_STACK_GROWSUP
        stack_base = vma->vm_start + stack_expand;
#else
        stack_base = vma->vm_end - stack_expand;
#endif
        current->mm->start_stack = bprm->p;
        ret = expand_stack_locked(vma, stack_base);
        if (ret)
                ret = -EFAULT;

out_unlock:
        mmap_write_unlock(mm);
        return ret;
}
EXPORT_SYMBOL(setup_arg_pages);

#else

/*
 * Transfer the program arguments and environment from the holding pages
 * onto the stack. The provided stack pointer is adjusted accordingly.
 */
int transfer_args_to_stack(struct linux_binprm *bprm,
                           unsigned long *sp_location)
{
        unsigned long index, stop, sp;
        int ret = 0;

        stop = bprm->p >> PAGE_SHIFT;
        sp = *sp_location;

        for (index = MAX_ARG_PAGES - 1; index >= stop; index--) {
                unsigned int offset = index == stop ? bprm->p & ~PAGE_MASK : 0;
                char *src = kmap_local_page(bprm->page[index]) + offset;
                sp -= PAGE_SIZE - offset;
                if (copy_to_user((void *) sp, src, PAGE_SIZE - offset) != 0)
                        ret = -EFAULT;
                kunmap_local(src);
                if (ret)
                        goto out;
        }

        *sp_location = sp;

out:
        return ret;
}
EXPORT_SYMBOL(transfer_args_to_stack);

#endif /* CONFIG_MMU */

static struct file *do_open_execat(int fd, struct filename *name, int flags)
{
        struct file *file;
        int err;
        struct open_flags open_exec_flags = {
                .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC,
                .acc_mode = MAY_EXEC,
                .intent = LOOKUP_OPEN,
                .lookup_flags = LOOKUP_FOLLOW,
        };

        if ((flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
                return ERR_PTR(-EINVAL);
        if (flags & AT_SYMLINK_NOFOLLOW)
                open_exec_flags.lookup_flags &= ~LOOKUP_FOLLOW;
        if (flags & AT_EMPTY_PATH)
                open_exec_flags.lookup_flags |= LOOKUP_EMPTY;

        file = do_filp_open(fd, name, &open_exec_flags);
        if (IS_ERR(file))
                goto out;

        /*
         * may_open() has already checked for this, so it should be
         * impossible to trip now. But we need to be extra cautious
         * and check again at the very end too.
         */
        err = -EACCES;
        if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) ||
                         path_noexec(&file->f_path)))
                goto exit;

        err = deny_write_access(file);
        if (err)
                goto exit;

out:
        return file;

exit:
        fput(file);
        return ERR_PTR(err);
}

struct file *open_exec(const char *name)
{
        struct filename *filename = getname_kernel(name);
        struct file *f = ERR_CAST(filename);

        if (!IS_ERR(filename)) {
                f = do_open_execat(AT_FDCWD, filename, 0);
                putname(filename);
        }
        return f;
}
EXPORT_SYMBOL(open_exec);

#if defined(CONFIG_BINFMT_FLAT) || defined(CONFIG_BINFMT_ELF_FDPIC)
ssize_t read_code(struct file *file, unsigned long addr, loff_t pos, size_t len)
{
        ssize_t res = vfs_read(file, (void __user *)addr, len, &pos);
        if (res > 0)
                flush_icache_user_range(addr, addr + len);
        return res;
}
EXPORT_SYMBOL(read_code);
#endif

/*
 * Maps the mm_struct mm into the current task struct.
 * On success, this function returns with exec_update_lock
 * held for writing.
 */
static int exec_mmap(struct mm_struct *mm)
{
        struct task_struct *tsk;
        struct mm_struct *old_mm, *active_mm;
        int ret;

        /* Notify parent that we're no longer interested in the old VM */
        tsk = current;
        old_mm = current->mm;
        exec_mm_release(tsk, old_mm);

        ret = down_write_killable(&tsk->signal->exec_update_lock);
        if (ret)
                return ret;

        if (old_mm) {
                /*
                 * If there is a pending fatal signal perhaps a signal
                 * whose default action is to create a coredump get
                 * out and die instead of going through with the exec.
                 */
                ret = mmap_read_lock_killable(old_mm);

                if (ret) {
                        up_write(&tsk->signal->exec_update_lock);
                        return ret;
                }
        }

        task_lock(tsk);
        membarrier_exec_mmap(mm);

        local_irq_disable();
        active_mm = tsk->active_mm;
        tsk->active_mm = mm;
        tsk->mm = mm;
        mm_init_cid(mm);
        /*
         * This prevents preemption while active_mm is being loaded and
         * it and mm are being updated, which could cause problems for
         * lazy tlb mm refcounting when these are updated by context
         * switches. Not all architectures can handle irqs off over
         * activate_mm yet.
         */
        if (!IS_ENABLED(CONFIG_ARCH_WANT_IRQS_OFF_ACTIVATE_MM))
                local_irq_enable();
        activate_mm(active_mm, mm);
        if (IS_ENABLED(CONFIG_ARCH_WANT_IRQS_OFF_ACTIVATE_MM))
                local_irq_enable();
        lru_gen_add_mm(mm);
        task_unlock(tsk);
        lru_gen_use_mm(mm);
        if (old_mm) {
                mmap_read_unlock(old_mm);
                BUG_ON(active_mm != old_mm);
                setmax_mm_hiwater_rss(&tsk->signal->maxrss, old_mm);
                mm_update_next_owner(old_mm);
                mmput(old_mm);
                return 0;
        }
        mmdrop_lazy_tlb(active_mm);
        return 0;
}

static int de_thread(struct task_struct *tsk)
{
        struct signal_struct *sig = tsk->signal;
        struct sighand_struct *oldsighand = tsk->sighand;
        spinlock_t *lock = &oldsighand->siglock;

        if (thread_group_empty(tsk))
                goto no_thread_group;

        /*
         * Kill all other threads in the thread group.
         */
        spin_lock_irq(lock);
        if ((sig->flags & SIGNAL_GROUP_EXIT) || sig->group_exec_task) {
                /*
                 * Another group action in progress, just
                 * return so that the signal is processed.
                 */
                spin_unlock_irq(lock);
                return -EAGAIN;
        }

        sig->group_exec_task = tsk;
        sig->notify_count = zap_other_threads(tsk);
        if (!thread_group_leader(tsk))
                sig->notify_count--;

        while (sig->notify_count) {
                __set_current_state(TASK_KILLABLE);
                spin_unlock_irq(lock);
                schedule();
                if (__fatal_signal_pending(tsk))
                        goto killed;
                spin_lock_irq(lock);
        }
        spin_unlock_irq(lock);

        /*
         * At this point all other threads have exited, all we have to
         * do is to wait for the thread group leader to become inactive,
         * and to assume its PID:
         */
        if (!thread_group_leader(tsk)) {
                struct task_struct *leader = tsk->group_leader;

                for (;;) {
                        cgroup_threadgroup_change_begin(tsk);
                        write_lock_irq(&tasklist_lock);
                        /*
                         * Do this under tasklist_lock to ensure that
                         * exit_notify() can't miss ->group_exec_task
                         */
                        sig->notify_count = -1;
                        if (likely(leader->exit_state))
                                break;
                        __set_current_state(TASK_KILLABLE);
                        write_unlock_irq(&tasklist_lock);
                        cgroup_threadgroup_change_end(tsk);
                        schedule();
                        if (__fatal_signal_pending(tsk))
                                goto killed;
                }

                /*
                 * The only record we have of the real-time age of a
                 * process, regardless of execs it's done, is start_time.
                 * All the past CPU time is accumulated in signal_struct
                 * from sister threads now dead.  But in this non-leader
                 * exec, nothing survives from the original leader thread,
                 * whose birth marks the true age of this process now.
                 * When we take on its identity by switching to its PID, we
                 * also take its birthdate (always earlier than our own).
                 */
                tsk->start_time = leader->start_time;
                tsk->start_boottime = leader->start_boottime;

                BUG_ON(!same_thread_group(leader, tsk));
                /*
                 * An exec() starts a new thread group with the
                 * TGID of the previous thread group. Rehash the
                 * two threads with a switched PID, and release
                 * the former thread group leader:
                 */

                /* Become a process group leader with the old leader's pid.
                 * The old leader becomes a thread of the this thread group.
                 */
                exchange_tids(tsk, leader);
                transfer_pid(leader, tsk, PIDTYPE_TGID);
                transfer_pid(leader, tsk, PIDTYPE_PGID);
                transfer_pid(leader, tsk, PIDTYPE_SID);

                list_replace_rcu(&leader->tasks, &tsk->tasks);
                list_replace_init(&leader->sibling, &tsk->sibling);

                tsk->group_leader = tsk;
                leader->group_leader = tsk;

                tsk->exit_signal = SIGCHLD;
                leader->exit_signal = -1;

                BUG_ON(leader->exit_state != EXIT_ZOMBIE);
                leader->exit_state = EXIT_DEAD;

                /*
                 * We are going to release_task()->ptrace_unlink() silently,
                 * the tracer can sleep in do_wait(). EXIT_DEAD guarantees
                 * the tracer won't block again waiting for this thread.
                 */
                if (unlikely(leader->ptrace))
                        __wake_up_parent(leader, leader->parent);
                write_unlock_irq(&tasklist_lock);
                cgroup_threadgroup_change_end(tsk);

                release_task(leader);
        }

        sig->group_exec_task = NULL;
        sig->notify_count = 0;

no_thread_group:
        /* we have changed execution domain */
        tsk->exit_signal = SIGCHLD;

        BUG_ON(!thread_group_leader(tsk));
        return 0;

killed:
        /* protects against exit_notify() and __exit_signal() */
        read_lock(&tasklist_lock);
        sig->group_exec_task = NULL;
        sig->notify_count = 0;
        read_unlock(&tasklist_lock);
        return -EAGAIN;
}


/*
 * This function makes sure the current process has its own signal table,
 * so that flush_signal_handlers can later reset the handlers without
 * disturbing other processes.  (Other processes might share the signal
 * table via the CLONE_SIGHAND option to clone().)
 */
static int unshare_sighand(struct task_struct *me)
{
        struct sighand_struct *oldsighand = me->sighand;

        if (refcount_read(&oldsighand->count) != 1) {
                struct sighand_struct *newsighand;
                /*
                 * This ->sighand is shared with the CLONE_SIGHAND
                 * but not CLONE_THREAD task, switch to the new one.
                 */
                newsighand = kmem_cache_alloc(sighand_cachep, GFP_KERNEL);
                if (!newsighand)
                        return -ENOMEM;

                refcount_set(&newsighand->count, 1);

                write_lock_irq(&tasklist_lock);
                spin_lock(&oldsighand->siglock);
                memcpy(newsighand->action, oldsighand->action,
                       sizeof(newsighand->action));
                rcu_assign_pointer(me->sighand, newsighand);
                spin_unlock(&oldsighand->siglock);
                write_unlock_irq(&tasklist_lock);

                __cleanup_sighand(oldsighand);
        }
        return 0;
}

char *__get_task_comm(char *buf, size_t buf_size, struct task_struct *tsk)
{
        task_lock(tsk);
        /* Always NUL terminated and zero-padded */
        strscpy_pad(buf, tsk->comm, buf_size);
        task_unlock(tsk);
        return buf;
}
EXPORT_SYMBOL_GPL(__get_task_comm);

/*
 * These functions flushes out all traces of the currently running executable
 * so that a new one can be started
 */

void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
{
        task_lock(tsk);
        trace_task_rename(tsk, buf);
        strscpy_pad(tsk->comm, buf, sizeof(tsk->comm));
        task_unlock(tsk);
        perf_event_comm(tsk, exec);
}

/*
 * Calling this is the point of no return. None of the failures will be
 * seen by userspace since either the process is already taking a fatal
 * signal (via de_thread() or coredump), or will have SEGV raised
 * (after exec_mmap()) by search_binary_handler (see below).
 */
int begin_new_exec(struct linux_binprm * bprm)
{
        struct task_struct *me = current;
        int retval;

        /* Once we are committed compute the creds */
        retval = bprm_creds_from_file(bprm);
        if (retval)
                return retval;

        /*
         * Ensure all future errors are fatal.
         */
        bprm->point_of_no_return = true;

        /*
         * Make this the only thread in the thread group.
         */
        retval = de_thread(me);
        if (retval)
                goto out;

        /*
         * Cancel any io_uring activity across execve
         */
        io_uring_task_cancel();

        /* Ensure the files table is not shared. */
        retval = unshare_files();
        if (retval)
                goto out;

        /*
         * Must be called _before_ exec_mmap() as bprm->mm is
         * not visible until then. Doing it here also ensures
         * we don't race against replace_mm_exe_file().
         */
        retval = set_mm_exe_file(bprm->mm, bprm->file);
        if (retval)
                goto out;

        /* If the binary is not readable then enforce mm->dumpable=0 */
        would_dump(bprm, bprm->file);
        if (bprm->have_execfd)
                would_dump(bprm, bprm->executable);

        /*
         * Release all of the old mmap stuff
         */
        acct_arg_size(bprm, 0);
        retval = exec_mmap(bprm->mm);
        if (retval)
                goto out;

        bprm->mm = NULL;

        retval = exec_task_namespaces();
        if (retval)
                goto out_unlock;

#ifdef CONFIG_POSIX_TIMERS
        spin_lock_irq(&me->sighand->siglock);
        posix_cpu_timers_exit(me);
        spin_unlock_irq(&me->sighand->siglock);
        exit_itimers(me);
        flush_itimer_signals();
#endif

        /*
         * Make the signal table private.
         */
        retval = unshare_sighand(me);
        if (retval)
                goto out_unlock;

        me->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC |
                                        PF_NOFREEZE | PF_NO_SETAFFINITY);
        flush_thread();
        me->personality &= ~bprm->per_clear;

        clear_syscall_work_syscall_user_dispatch(me);

        /*
         * We have to apply CLOEXEC before we change whether the process is
         * dumpable (in setup_new_exec) to avoid a race with a process in userspace
         * trying to access the should-be-closed file descriptors of a process
         * undergoing exec(2).
         */
        do_close_on_exec(me->files);

        if (bprm->secureexec) {
                /* Make sure parent cannot signal privileged process. */
                me->pdeath_signal = 0;

                /*
                 * For secureexec, reset the stack limit to sane default to
                 * avoid bad behavior from the prior rlimits. This has to
                 * happen before arch_pick_mmap_layout(), which examines
                 * RLIMIT_STACK, but after the point of no return to avoid
                 * needing to clean up the change on failure.
                 */
                if (bprm->rlim_stack.rlim_cur > _STK_LIM)
                        bprm->rlim_stack.rlim_cur = _STK_LIM;
        }

        me->sas_ss_sp = me->sas_ss_size = 0;

        /*
         * Figure out dumpability. Note that this checking only of current
         * is wrong, but userspace depends on it. This should be testing
         * bprm->secureexec instead.
         */
        if (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP ||
            !(uid_eq(current_euid(), current_uid()) &&
              gid_eq(current_egid(), current_gid())))
                set_dumpable(current->mm, suid_dumpable);
        else
                set_dumpable(current->mm, SUID_DUMP_USER);

        perf_event_exec();
        __set_task_comm(me, kbasename(bprm->filename), true);

        /* An exec changes our domain. We are no longer part of the thread
           group */
        WRITE_ONCE(me->self_exec_id, me->self_exec_id + 1);
        flush_signal_handlers(me, 0);

        retval = set_cred_ucounts(bprm->cred);
        if (retval < 0)
                goto out_unlock;

        /*
         * install the new credentials for this executable
         */
        security_bprm_committing_creds(bprm);

        commit_creds(bprm->cred);
        bprm->cred = NULL;

        /*
         * Disable monitoring for regular users
         * when executing setuid binaries. Must
         * wait until new credentials are committed
         * by commit_creds() above
         */
        if (get_dumpable(me->mm) != SUID_DUMP_USER)
                perf_event_exit_task(me);
        /*
         * cred_guard_mutex must be held at least to this point to prevent
         * ptrace_attach() from altering our determination of the task's
         * credentials; any time after this it may be unlocked.
         */
        security_bprm_committed_creds(bprm);

        /* Pass the opened binary to the interpreter. */
        if (bprm->have_execfd) {
                retval = get_unused_fd_flags(0);
                if (retval < 0)
                        goto out_unlock;
                fd_install(retval, bprm->executable);
                bprm->executable = NULL;
                bprm->execfd = retval;
        }
        return 0;

out_unlock:
        up_write(&me->signal->exec_update_lock);
out:
        return retval;
}
EXPORT_SYMBOL(begin_new_exec);

void would_dump(struct linux_binprm *bprm, struct file *file)
{
        struct inode *inode = file_inode(file);
        struct mnt_idmap *idmap = file_mnt_idmap(file);
        if (inode_permission(idmap, inode, MAY_READ) < 0) {
                struct user_namespace *old, *user_ns;
                bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;

                /* Ensure mm->user_ns contains the executable */
                user_ns = old = bprm->mm->user_ns;
                while ((user_ns != &init_user_ns) &&
                       !privileged_wrt_inode_uidgid(user_ns, idmap, inode))
                        user_ns = user_ns->parent;

                if (old != user_ns) {
                        bprm->mm->user_ns = get_user_ns(user_ns);
                        put_user_ns(old);
                }
        }
}
EXPORT_SYMBOL(would_dump);

void setup_new_exec(struct linux_binprm * bprm)
{
        /* Setup things that can depend upon the personality */
        struct task_struct *me = current;

        arch_pick_mmap_layout(me->mm, &bprm->rlim_stack);

        arch_setup_new_exec();

        /* Set the new mm task size. We have to do that late because it may
         * depend on TIF_32BIT which is only updated in flush_thread() on
         * some architectures like powerpc
         */
        me->mm->task_size = TASK_SIZE;
        up_write(&me->signal->exec_update_lock);
        mutex_unlock(&me->signal->cred_guard_mutex);
}
EXPORT_SYMBOL(setup_new_exec);

/* Runs immediately before start_thread() takes over. */
void finalize_exec(struct linux_binprm *bprm)
{
        /* Store any stack rlimit changes before starting thread. */
        task_lock(current->group_leader);
        current->signal->rlim[RLIMIT_STACK] = bprm->rlim_stack;
        task_unlock(current->group_leader);
}
EXPORT_SYMBOL(finalize_exec);

/*
 * Prepare credentials and lock ->cred_guard_mutex.
 * setup_new_exec() commits the new creds and drops the lock.
 * Or, if exec fails before, free_bprm() should release ->cred
 * and unlock.
 */
static int prepare_bprm_creds(struct linux_binprm *bprm)
{
        if (mutex_lock_interruptible(&current->signal->cred_guard_mutex))
                return -ERESTARTNOINTR;

        bprm->cred = prepare_exec_creds();
        if (likely(bprm->cred))
                return 0;

        mutex_unlock(&current->signal->cred_guard_mutex);
        return -ENOMEM;
}

static void free_bprm(struct linux_binprm *bprm)
{
        if (bprm->mm) {
                acct_arg_size(bprm, 0);
                mmput(bprm->mm);
        }
        free_arg_pages(bprm);
        if (bprm->cred) {
                mutex_unlock(&current->signal->cred_guard_mutex);
                abort_creds(bprm->cred);
        }
        if (bprm->file) {
                allow_write_access(bprm->file);
                fput(bprm->file);
        }
        if (bprm->executable)
                fput(bprm->executable);
        /* If a binfmt changed the interp, free it. */
        if (bprm->interp != bprm->filename)
                kfree(bprm->interp);
        kfree(bprm->fdpath);
        kfree(bprm);
}

static struct linux_binprm *alloc_bprm(int fd, struct filename *filename)
{
        struct linux_binprm *bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
        int retval = -ENOMEM;
        if (!bprm)
                goto out;

        if (fd == AT_FDCWD || filename->name[0] == '/') {
                bprm->filename = filename->name;
        } else {
                if (filename->name[0] == '\0')
                        bprm->fdpath = kasprintf(GFP_KERNEL, "/dev/fd/%d", fd);
                else
                        bprm->fdpath = kasprintf(GFP_KERNEL, "/dev/fd/%d/%s",
                                                  fd, filename->name);
                if (!bprm->fdpath)
                        goto out_free;

                bprm->filename = bprm->fdpath;
        }
        bprm->interp = bprm->filename;

        retval = bprm_mm_init(bprm);
        if (retval)
                goto out_free;
        return bprm;

out_free:
        free_bprm(bprm);
out:
        return ERR_PTR(retval);
}

int bprm_change_interp(const char *interp, struct linux_binprm *bprm)
{
        /* If a binfmt changed the interp, free it first. */
        if (bprm->interp != bprm->filename)
                kfree(bprm->interp);
        bprm->interp = kstrdup(interp, GFP_KERNEL);
        if (!bprm->interp)
                return -ENOMEM;
        return 0;
}
EXPORT_SYMBOL(bprm_change_interp);

/*
 * determine how safe it is to execute the proposed program
 * - the caller must hold ->cred_guard_mutex to protect against
 *   PTRACE_ATTACH or seccomp thread-sync
 */
static void check_unsafe_exec(struct linux_binprm *bprm)
{
        struct task_struct *p = current, *t;
        unsigned n_fs;

        if (p->ptrace)
                bprm->unsafe |= LSM_UNSAFE_PTRACE;

        /*
         * This isn't strictly necessary, but it makes it harder for LSMs to
         * mess up.
         */
        if (task_no_new_privs(current))
                bprm->unsafe |= LSM_UNSAFE_NO_NEW_PRIVS;

        /*
         * If another task is sharing our fs, we cannot safely
         * suid exec because the differently privileged task
         * will be able to manipulate the current directory, etc.
         * It would be nice to force an unshare instead...
         */
        t = p;
        n_fs = 1;
        spin_lock(&p->fs->lock);
        rcu_read_lock();
        while_each_thread(p, t) {
                if (t->fs == p->fs)
                        n_fs++;
        }
        rcu_read_unlock();

        if (p->fs->users > n_fs)
                bprm->unsafe |= LSM_UNSAFE_SHARE;
        else
                p->fs->in_exec = 1;
        spin_unlock(&p->fs->lock);
}

static void bprm_fill_uid(struct linux_binprm *bprm, struct file *file)
{
        /* Handle suid and sgid on files */
        struct mnt_idmap *idmap;
        struct inode *inode = file_inode(file);
        unsigned int mode;
        vfsuid_t vfsuid;
        vfsgid_t vfsgid;

        if (!mnt_may_suid(file->f_path.mnt))
                return;

        if (task_no_new_privs(current))
                return;

        mode = READ_ONCE(inode->i_mode);
        if (!(mode & (S_ISUID|S_ISGID)))
                return;

        idmap = file_mnt_idmap(file);

        /* Be careful if suid/sgid is set */
        inode_lock(inode);

        /* reload atomically mode/uid/gid now that lock held */
        mode = inode->i_mode;
        vfsuid = i_uid_into_vfsuid(idmap, inode);
        vfsgid = i_gid_into_vfsgid(idmap, inode);
        inode_unlock(inode);

        /* We ignore suid/sgid if there are no mappings for them in the ns */
        if (!vfsuid_has_mapping(bprm->cred->user_ns, vfsuid) ||
            !vfsgid_has_mapping(bprm->cred->user_ns, vfsgid))
                return;

        if (mode & S_ISUID) {
                bprm->per_clear |= PER_CLEAR_ON_SETID;
                bprm->cred->euid = vfsuid_into_kuid(vfsuid);
        }

        if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
                bprm->per_clear |= PER_CLEAR_ON_SETID;
                bprm->cred->egid = vfsgid_into_kgid(vfsgid);
        }
}

/*
 * Compute brpm->cred based upon the final binary.
 */
static int bprm_creds_from_file(struct linux_binprm *bprm)
{
        /* Compute creds based on which file? */
        struct file *file = bprm->execfd_creds ? bprm->executable : bprm->file;

        bprm_fill_uid(bprm, file);
        return security_bprm_creds_from_file(bprm, file);
}

/*
 * Fill the binprm structure from the inode.
 * Read the first BINPRM_BUF_SIZE bytes
 *
 * This may be called multiple times for binary chains (scripts for example).
 */
static int prepare_binprm(struct linux_binprm *bprm)
{
        loff_t pos = 0;

        memset(bprm->buf, 0, BINPRM_BUF_SIZE);
        return kernel_read(bprm->file, bprm->buf, BINPRM_BUF_SIZE, &pos);
}

/*
 * Arguments are '\0' separated strings found at the location bprm->p
 * points to; chop off the first by relocating brpm->p to right after
 * the first '\0' encountered.
 */
int remove_arg_zero(struct linux_binprm *bprm)
{
        int ret = 0;
        unsigned long offset;
        char *kaddr;
        struct page *page;

        if (!bprm->argc)
                return 0;

        do {
                offset = bprm->p & ~PAGE_MASK;
                page = get_arg_page(bprm, bprm->p, 0);
                if (!page) {
                        ret = -EFAULT;
                        goto out;
                }
                kaddr = kmap_local_page(page);

                for (; offset < PAGE_SIZE && kaddr[offset];
                                offset++, bprm->p++)
                        ;

                kunmap_local(kaddr);
                put_arg_page(page);
        } while (offset == PAGE_SIZE);

        bprm->p++;
        bprm->argc--;
        ret = 0;

out:
        return ret;
}
EXPORT_SYMBOL(remove_arg_zero);

#define printable(c) (((c)=='\t') || ((c)=='\n') || (0x20<=(c) && (c)<=0x7e))
/*
 * cycle the list of binary formats handler, until one recognizes the image
 */
static int search_binary_handler(struct linux_binprm *bprm)
{
        bool need_retry = IS_ENABLED(CONFIG_MODULES);
        struct linux_binfmt *fmt;
        int retval;

        retval = prepare_binprm(bprm);
        if (retval < 0)
                return retval;

        retval = security_bprm_check(bprm);
        if (retval)
                return retval;

        retval = -ENOENT;
 retry:
        read_lock(&binfmt_lock);
        list_for_each_entry(fmt, &formats, lh) {
                if (!try_module_get(fmt->module))
                        continue;
                read_unlock(&binfmt_lock);

                retval = fmt->load_binary(bprm);

                read_lock(&binfmt_lock);
                put_binfmt(fmt);
                if (bprm->point_of_no_return || (retval != -ENOEXEC)) {
                        read_unlock(&binfmt_lock);
                        return retval;
                }
        }
        read_unlock(&binfmt_lock);

        if (need_retry) {
                if (printable(bprm->buf[0]) && printable(bprm->buf[1]) &&
                    printable(bprm->buf[2]) && printable(bprm->buf[3]))
                        return retval;
                if (request_module("binfmt-%04x", *(ushort *)(bprm->buf + 2)) < 0)
                        return retval;
                need_retry = false;
                goto retry;
        }

        return retval;
}

/* binfmt handlers will call back into begin_new_exec() on success. */
static int exec_binprm(struct linux_binprm *bprm)
{
        pid_t old_pid, old_vpid;
        int ret, depth;

        /* Need to fetch pid before load_binary changes it */
        old_pid = current->pid;
        rcu_read_lock();
        old_vpid = task_pid_nr_ns(current, task_active_pid_ns(current->parent));
        rcu_read_unlock();

        /* This allows 4 levels of binfmt rewrites before failing hard. */
        for (depth = 0;; depth++) {
                struct file *exec;
                if (depth > 5)
                        return -ELOOP;

                ret = search_binary_handler(bprm);
                if (ret < 0)
                        return ret;
                if (!bprm->interpreter)
                        break;

                exec = bprm->file;
                bprm->file = bprm->interpreter;
                bprm->interpreter = NULL;

                allow_write_access(exec);
                if (unlikely(bprm->have_execfd)) {
                        if (bprm->executable) {
                                fput(exec);
                                return -ENOEXEC;
                        }
                        bprm->executable = exec;
                } else
                        fput(exec);
        }

        audit_bprm(bprm);
        trace_sched_process_exec(current, old_pid, bprm);
        ptrace_event(PTRACE_EVENT_EXEC, old_vpid);
        proc_exec_connector(current);
        return 0;
}

/*
 * sys_execve() executes a new program.
 */
static int bprm_execve(struct linux_binprm *bprm,
                       int fd, struct filename *filename, int flags)
{
        struct file *file;
        int retval;

        retval = prepare_bprm_creds(bprm);
        if (retval)
                return retval;

        /*
         * Check for unsafe execution states before exec_binprm(), which
         * will call back into begin_new_exec(), into bprm_creds_from_file(),
         * where setuid-ness is evaluated.
         */
        check_unsafe_exec(bprm);
        current->in_execve = 1;
        sched_mm_cid_before_execve(current);

        file = do_open_execat(fd, filename, flags);
        retval = PTR_ERR(file);
        if (IS_ERR(file))
                goto out_unmark;

        sched_exec();

        bprm->file = file;
        /*
         * Record that a name derived from an O_CLOEXEC fd will be
         * inaccessible after exec.  This allows the code in exec to
         * choose to fail when the executable is not mmaped into the
         * interpreter and an open file descriptor is not passed to
         * the interpreter.  This makes for a better user experience
         * than having the interpreter start and then immediately fail
         * when it finds the executable is inaccessible.
         */
        if (bprm->fdpath && get_close_on_exec(fd))
                bprm->interp_flags |= BINPRM_FLAGS_PATH_INACCESSIBLE;

        /* Set the unchanging part of bprm->cred */
        retval = security_bprm_creds_for_exec(bprm);
        if (retval)
                goto out;

        retval = exec_binprm(bprm);
        if (retval < 0)
                goto out;

        sched_mm_cid_after_execve(current);
        /* execve succeeded */
        current->fs->in_exec = 0;
        current->in_execve = 0;
        rseq_execve(current);
        user_events_execve(current);
        acct_update_integrals(current);
        task_numa_free(current, false);
        return retval;

out:
        /*
         * If past the point of no return ensure the code never
         * returns to the userspace process.  Use an existing fatal
         * signal if present otherwise terminate the process with
         * SIGSEGV.
         */
        if (bprm->point_of_no_return && !fatal_signal_pending(current))
                force_fatal_sig(SIGSEGV);

out_unmark:
        sched_mm_cid_after_execve(current);
        current->fs->in_exec = 0;
        current->in_execve = 0;

        return retval;
}

static int do_execveat_common(int fd, struct filename *filename,
                              struct user_arg_ptr argv,
                              struct user_arg_ptr envp,
                              int flags)
{
        struct linux_binprm *bprm;
        int retval;

        if (IS_ERR(filename))
                return PTR_ERR(filename);

        /*
         * We move the actual failure in case of RLIMIT_NPROC excess from
         * set*uid() to execve() because too many poorly written programs
         * don't check setuid() return code.  Here we additionally recheck
         * whether NPROC limit is still exceeded.
         */
        if ((current->flags & PF_NPROC_EXCEEDED) &&
            is_rlimit_overlimit(current_ucounts(), UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC))) {
                retval = -EAGAIN;
                goto out_ret;
        }

        /* We're below the limit (still or again), so we don't want to make
         * further execve() calls fail. */
        current->flags &= ~PF_NPROC_EXCEEDED;

        bprm = alloc_bprm(fd, filename);
        if (IS_ERR(bprm)) {
                retval = PTR_ERR(bprm);
                goto out_ret;
        }

        retval = count(argv, MAX_ARG_STRINGS);
        if (retval == 0)
                pr_warn_once("process '%s' launched '%s' with NULL argv: empty string added\n",
                             current->comm, bprm->filename);
        if (retval < 0)
                goto out_free;
        bprm->argc = retval;

        retval = count(envp, MAX_ARG_STRINGS);
        if (retval < 0)
                goto out_free;
        bprm->envc = retval;

        retval = bprm_stack_limits(bprm);
        if (retval < 0)
                goto out_free;

        retval = copy_string_kernel(bprm->filename, bprm);
        if (retval < 0)
                goto out_free;
        bprm->exec = bprm->p;

        retval = copy_strings(bprm->envc, envp, bprm);
        if (retval < 0)
                goto out_free;

        retval = copy_strings(bprm->argc, argv, bprm);
        if (retval < 0)
                goto out_free;

        /*
         * When argv is empty, add an empty string ("") as argv[0] to
         * ensure confused userspace programs that start processing
         * from argv[1] won't end up walking envp. See also
         * bprm_stack_limits().
         */
        if (bprm->argc == 0) {
                retval = copy_string_kernel("", bprm);
                if (retval < 0)
                        goto out_free;
                bprm->argc = 1;
        }

        retval = bprm_execve(bprm, fd, filename, flags);
out_free:
        free_bprm(bprm);

out_ret:
        putname(filename);
        return retval;
}

int kernel_execve(const char *kernel_filename,
                  const char *const *argv, const char *const *envp)
{
        struct filename *filename;
        struct linux_binprm *bprm;
        int fd = AT_FDCWD;
        int retval;

        /* It is non-sense for kernel threads to call execve */
        if (WARN_ON_ONCE(current->flags & PF_KTHREAD))
                return -EINVAL;

        filename = getname_kernel(kernel_filename);
        if (IS_ERR(filename))
                return PTR_ERR(filename);

        bprm = alloc_bprm(fd, filename);
        if (IS_ERR(bprm)) {
                retval = PTR_ERR(bprm);
                goto out_ret;
        }

        retval = count_strings_kernel(argv);
        if (WARN_ON_ONCE(retval == 0))
                retval = -EINVAL;
        if (retval < 0)
                goto out_free;
        bprm->argc = retval;

        retval = count_strings_kernel(envp);