/*
 *  binfmt_misc.c
 *
 *  Copyright (C) 1997 Richard Günther
 *
 *  binfmt_misc detects binaries via a magic or filename extension and invokes
 *  a specified wrapper. This should obsolete binfmt_java, binfmt_em86 and
 *  binfmt_mz.
 *
 *  1997-04-25 first version
 *  [...]
 *  1997-05-19 cleanup
 *  1997-06-26 hpa: pass the real filename rather than argv[0]
 *  1997-06-30 minor cleanup
 *  1997-08-09 removed extension stripping, locking cleanup
 *  2001-02-28 AV: rewritten into something that resembles C. Original didn't.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/binfmts.h>
#include <linux/slab.h>
#include <linux/ctype.h>
#include <linux/file.h>
#include <linux/pagemap.h>
#include <linux/namei.h>
#include <linux/mount.h>
#include <linux/syscalls.h>

#include <asm/uaccess.h>

enum {
        VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
};

static LIST_HEAD(entries);
static int enabled = 1;

enum {Enabled, Magic};
#define MISC_FMT_PRESERVE_ARGV0 (1<<31)
#define MISC_FMT_OPEN_BINARY (1<<30)
#define MISC_FMT_CREDENTIALS (1<<29)

typedef struct {
        struct list_head list;
        unsigned long flags;            /* type, status, etc. */
        int offset;                     /* offset of magic */
        int size;                       /* size of magic/mask */
        char *magic;                    /* magic or filename extension */
        char *mask;                     /* mask, NULL for exact match */
        char *interpreter;              /* filename of interpreter */
        char *name;
        struct dentry *dentry;
} Node;

static DEFINE_RWLOCK(entries_lock);
static struct file_system_type bm_fs_type;
static struct vfsmount *bm_mnt;
static int entry_count;

/* 
 * Check if we support the binfmt
 * if we do, return the node, else NULL
 * locking is done in load_misc_binary
 */
static Node *check_file(struct linux_binprm *bprm)
{
        char *p = strrchr(bprm->interp, '.');
        struct list_head *l;

        list_for_each(l, &entries) {
                Node *e = list_entry(l, Node, list);
                char *s;
                int j;

                if (!test_bit(Enabled, &e->flags))
                        continue;

                if (!test_bit(Magic, &e->flags)) {
                        if (p && !strcmp(e->magic, p + 1))
                                return e;
                        continue;
                }

                s = bprm->buf + e->offset;
                if (e->mask) {
                        for (j = 0; j < e->size; j++)
                                if ((*s++ ^ e->magic[j]) & e->mask[j])
                                        break;
                } else {
                        for (j = 0; j < e->size; j++)
                                if ((*s++ ^ e->magic[j]))
                                        break;
                }
                if (j == e->size)
                        return e;
        }
        return NULL;
}

/*
 * the loader itself
 */
static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
{
        Node *fmt;
        struct file * interp_file = NULL;
        char iname[BINPRM_BUF_SIZE];
        char *iname_addr = iname;
        int retval;
        int fd_binary = -1;
        struct files_struct *files = NULL;

        retval = -ENOEXEC;
        if (!enabled)
                goto _ret;

        /* to keep locking time low, we copy the interpreter string */
        read_lock(&entries_lock);
        fmt = check_file(bprm);
        if (fmt)
                strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
        read_unlock(&entries_lock);
        if (!fmt)
                goto _ret;

        if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
                remove_arg_zero(bprm);
        }

        if (fmt->flags & MISC_FMT_OPEN_BINARY) {

                files = current->files;
                retval = unshare_files();
                if (retval < 0)
                        goto _ret;
                if (files == current->files) {
                        put_files_struct(files);
                        files = NULL;
                }
                /* if the binary should be opened on behalf of the
                 * interpreter than keep it open and assign descriptor
                 * to it */
                fd_binary = get_unused_fd();
                if (fd_binary < 0) {
                        retval = fd_binary;
                        goto _unshare;
                }
                fd_install(fd_binary, bprm->file);

                /* if the binary is not readable than enforce mm->dumpable=0
                   regardless of the interpreter's permissions */
                if (file_permission(bprm->file, MAY_READ))
                        bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;

                allow_write_access(bprm->file);
                bprm->file = NULL;

                /* mark the bprm that fd should be passed to interp */
                bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
                bprm->interp_data = fd_binary;

        } else {
                allow_write_access(bprm->file);
                fput(bprm->file);
                bprm->file = NULL;
        }
        /* make argv[1] be the path to the binary */
        retval = copy_strings_kernel (1, &bprm->interp, bprm);
        if (retval < 0)
                goto _error;
        bprm->argc++;

        /* add the interp as argv[0] */
        retval = copy_strings_kernel (1, &iname_addr, bprm);
        if (retval < 0)
                goto _error;
        bprm->argc ++;

        bprm->interp = iname;   /* for binfmt_script */

        interp_file = open_exec (iname);
        retval = PTR_ERR (interp_file);
        if (IS_ERR (interp_file))
                goto _error;

        bprm->file = interp_file;
        if (fmt->flags & MISC_FMT_CREDENTIALS) {
                /*
                 * No need to call prepare_binprm(), it's already been
                 * done.  bprm->buf is stale, update from interp_file.
                 */
                memset(bprm->buf, 0, BINPRM_BUF_SIZE);
                retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
        } else
                retval = prepare_binprm (bprm);

        if (retval < 0)
                goto _error;

        retval = search_binary_handler (bprm, regs);
        if (retval < 0)
                goto _error;

        if (files) {
                put_files_struct(files);
                files = NULL;
        }
_ret:
        return retval;
_error:
        if (fd_binary > 0)
                sys_close(fd_binary);
        bprm->interp_flags = 0;
        bprm->interp_data = 0;
_unshare:
        if (files)
                reset_files_struct(current, files);
        goto _ret;
}

/* Command parsers */

/*
 * parses and copies one argument enclosed in del from *sp to *dp,
 * recognising the \x special.
 * returns pointer to the copied argument or NULL in case of an
 * error (and sets err) or null argument length.
 */
static char *scanarg(char *s, char del)
{
        char c;

        while ((c = *s++) != del) {
                if (c == '\\' && *s == 'x') {
                        s++;
                        if (!isxdigit(*s++))
                                return NULL;
                        if (!isxdigit(*s++))
                                return NULL;
                }
        }
        return s;
}

static int unquote(char *from)
{
        char c = 0, *s = from, *p = from;

        while ((c = *s++) != '\0') {
                if (c == '\\' && *s == 'x') {
                        s++;
                        c = toupper(*s++);
                        *p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
                        c = toupper(*s++);
                        *p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
                        continue;
                }
                *p++ = c;
        }
        return p - from;
}

static char * check_special_flags (char * sfs, Node * e)
{
        char * p = sfs;
        int cont = 1;

        /* special flags */
        while (cont) {
                switch (*p) {
                        case 'P':
                                p++;
                                e->flags |= MISC_FMT_PRESERVE_ARGV0;
                                break;
                        case 'O':
                                p++;
                                e->flags |= MISC_FMT_OPEN_BINARY;
                                break;
                        case 'C':
                                p++;
                                /* this flags also implies the
                                   open-binary flag */
                                e->flags |= (MISC_FMT_CREDENTIALS |
                                                MISC_FMT_OPEN_BINARY);
                                break;
                        default:
                                cont = 0;
                }
        }

        return p;
}
/*
 * This registers a new binary format, it recognises the syntax
 * ':name:type:offset:magic:mask:interpreter:flags'
 * where the ':' is the IFS, that can be chosen with the first char
 */
static Node *create_entry(const char __user *buffer, size_t count)
{
        Node *e;
        int memsize, err;
        char *buf, *p;
        char del;

        /* some sanity checks */
        err = -EINVAL;
        if ((count < 11) || (count > 256))
                goto out;

        err = -ENOMEM;
        memsize = sizeof(Node) + count + 8;
        e = kmalloc(memsize, GFP_USER);
        if (!e)
                goto out;

        p = buf = (char *)e + sizeof(Node);

        memset(e, 0, sizeof(Node));
        if (copy_from_user(buf, buffer, count))
                goto Efault;

        del = *p++;     /* delimeter */

        memset(buf+count, del, 8);

        e->name = p;
        p = strchr(p, del);
        if (!p)
                goto Einval;
        *p++ = '\0';
        if (!e->name[0] ||
            !strcmp(e->name, ".") ||
            !strcmp(e->name, "..") ||
            strchr(e->name, '/'))
                goto Einval;
        switch (*p++) {
                case 'E': e->flags = 1<<Enabled; break;
                case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
                default: goto Einval;
        }
        if (*p++ != del)
                goto Einval;
        if (test_bit(Magic, &e->flags)) {
                char *s = strchr(p, del);
                if (!s)
                        goto Einval;
                *s++ = '\0';
                e->offset = simple_strtoul(p, &p, 10);
                if (*p++)
                        goto Einval;
                e->magic = p;
                p = scanarg(p, del);
                if (!p)
                        goto Einval;
                p[-1] = '\0';
                if (!e->magic[0])
                        goto Einval;
                e->mask = p;
                p = scanarg(p, del);
                if (!p)
                        goto Einval;
                p[-1] = '\0';
                if (!e->mask[0])
                        e->mask = NULL;
                e->size = unquote(e->magic);
                if (e->mask && unquote(e->mask) != e->size)
                        goto Einval;
                if (e->size + e->offset > BINPRM_BUF_SIZE)
                        goto Einval;
        } else {
                p = strchr(p, del);
                if (!p)
                        goto Einval;
                *p++ = '\0';
                e->magic = p;
                p = strchr(p, del);
                if (!p)
                        goto Einval;
                *p++ = '\0';
                if (!e->magic[0] || strchr(e->magic, '/'))
                        goto Einval;
                p = strchr(p, del);
                if (!p)
                        goto Einval;
                *p++ = '\0';
        }
        e->interpreter = p;
        p = strchr(p, del);
        if (!p)
                goto Einval;
        *p++ = '\0';
        if (!e->interpreter[0])
                goto Einval;


        p = check_special_flags (p, e);

        if (*p == '\n')
                p++;
        if (p != buf + count)
                goto Einval;
        return e;

out:
        return ERR_PTR(err);

Efault:
        kfree(e);
        return ERR_PTR(-EFAULT);
Einval:
        kfree(e);
        return ERR_PTR(-EINVAL);
}

/*
 * Set status of entry/binfmt_misc:
 * '1' enables, '0' disables and '-1' clears entry/binfmt_misc
 */
static int parse_command(const char __user *buffer, size_t count)
{
        char s[4];

        if (!count)
                return 0;
        if (count > 3)
                return -EINVAL;
        if (copy_from_user(s, buffer, count))
                return -EFAULT;
        if (s[count-1] == '\n')
                count--;
        if (count == 1 && s[0] == '0')
                return 1;
        if (count == 1 && s[0] == '1')
                return 2;
        if (count == 2 && s[0] == '-' && s[1] == '1')
                return 3;
        return -EINVAL;
}

/* generic stuff */

static void entry_status(Node *e, char *page)
{
        char *dp;
        char *status = "disabled";
        const char * flags = "flags: ";

        if (test_bit(Enabled, &e->flags))
                status = "enabled";

        if (!VERBOSE_STATUS) {
                sprintf(page, "%s\n", status);
                return;
        }

        sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
        dp = page + strlen(page);

        /* print the special flags */
        sprintf (dp, "%s", flags);
        dp += strlen (flags);
        if (e->flags & MISC_FMT_PRESERVE_ARGV0) {
                *dp ++ = 'P';
        }
        if (e->flags & MISC_FMT_OPEN_BINARY) {
                *dp ++ = 'O';
        }
        if (e->flags & MISC_FMT_CREDENTIALS) {
                *dp ++ = 'C';
        }
        *dp ++ = '\n';


        if (!test_bit(Magic, &e->flags)) {
                sprintf(dp, "extension .%s\n", e->magic);
        } else {
                int i;

                sprintf(dp, "offset %i\nmagic ", e->offset);
                dp = page + strlen(page);
                for (i = 0; i < e->size; i++) {
                        sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
                        dp += 2;
                }
                if (e->mask) {
                        sprintf(dp, "\nmask ");
                        dp += 6;
                        for (i = 0; i < e->size; i++) {
                                sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
                                dp += 2;
                        }
                }
                *dp++ = '\n';
                *dp = '\0';
        }
}

static struct inode *bm_get_inode(struct super_block *sb, int mode)
{
        struct inode * inode = new_inode(sb);

        if (inode) {
                inode->i_mode = mode;
                inode->i_uid = 0;
                inode->i_gid = 0;
                inode->i_blocks = 0;
                inode->i_atime = inode->i_mtime = inode->i_ctime =
                        current_fs_time(inode->i_sb);
        }
        return inode;
}

static void bm_clear_inode(struct inode *inode)
{
        kfree(inode->i_private);
}

static void kill_node(Node *e)
{
        struct dentry *dentry;

        write_lock(&entries_lock);
        dentry = e->dentry;
        if (dentry) {
                list_del_init(&e->list);
                e->dentry = NULL;
        }
        write_unlock(&entries_lock);

        if (dentry) {
                dentry->d_inode->i_nlink--;
                d_drop(dentry);
                dput(dentry);
                simple_release_fs(&bm_mnt, &entry_count);
        }
}

/* /<entry> */

static ssize_t
bm_entry_read(struct file * file, char __user * buf, size_t nbytes, loff_t *ppos)
{
        Node *e = file->f_path.dentry->d_inode->i_private;
        loff_t pos = *ppos;
        ssize_t res;
        char *page;
        int len;

        if (!(page = (char*) __get_free_page(GFP_KERNEL)))
                return -ENOMEM;

        entry_status(e, page);
        len = strlen(page);

        res = -EINVAL;
        if (pos < 0)
                goto out;
        res = 0;
        if (pos >= len)
                goto out;
        if (len < pos + nbytes)
                nbytes = len - pos;
        res = -EFAULT;
        if (copy_to_user(buf, page + pos, nbytes))
                goto out;
        *ppos = pos + nbytes;
        res = nbytes;
out:
        free_page((unsigned long) page);
        return res;
}

static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
                                size_t count, loff_t *ppos)
{
        struct dentry *root;
        Node *e = file->f_path.dentry->d_inode->i_private;
        int res = parse_command(buffer, count);

        switch (res) {
                case 1: clear_bit(Enabled, &e->flags);
                        break;
                case 2: set_bit(Enabled, &e->flags);
                        break;
                case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
                        mutex_lock(&root->d_inode->i_mutex);

                        kill_node(e);

                        mutex_unlock(&root->d_inode->i_mutex);
                        dput(root);
                        break;
                default: return res;
        }
        return count;
}

static const struct file_operations bm_entry_operations = {
        .read           = bm_entry_read,
        .write          = bm_entry_write,
};

/* /register */

static ssize_t bm_register_write(struct file *file, const char __user *buffer,
                               size_t count, loff_t *ppos)
{
        Node *e;
        struct inode *inode;
        struct dentry *root, *dentry;
        struct super_block *sb = file->f_path.mnt->mnt_sb;
        int err = 0;

        e = create_entry(buffer, count);

        if (IS_ERR(e))
                return PTR_ERR(e);

        root = dget(sb->s_root);
        mutex_lock(&root->d_inode->i_mutex);
        dentry = lookup_one_len(e->name, root, strlen(e->name));
        err = PTR_ERR(dentry);
        if (IS_ERR(dentry))
                goto out;

        err = -EEXIST;
        if (dentry->d_inode)
                goto out2;

        inode = bm_get_inode(sb, S_IFREG | 0644);

        err = -ENOMEM;
        if (!inode)
                goto out2;

        err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
        if (err) {
                iput(inode);
                inode = NULL;
                goto out2;
        }

        e->dentry = dget(dentry);
        inode->i_private = e;
        inode->i_fop = &bm_entry_operations;

        d_instantiate(dentry, inode);
        write_lock(&entries_lock);
        list_add(&e->list, &entries);
        write_unlock(&entries_lock);

        err = 0;
out2:
        dput(dentry);
out:
        mutex_unlock(&root->d_inode->i_mutex);
        dput(root);

        if (err) {
                kfree(e);
                return -EINVAL;
        }
        return count;
}

static const struct file_operations bm_register_operations = {
        .write          = bm_register_write,
};

/* /status */

static ssize_t
bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
{
        char *s = enabled ? "enabled" : "disabled";

        return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
}

static ssize_t bm_status_write(struct file * file, const char __user * buffer,
                size_t count, loff_t *ppos)
{
        int res = parse_command(buffer, count);
        struct dentry *root;

        switch (res) {
                case 1: enabled = 0; break;
                case 2: enabled = 1; break;
                case 3: root = dget(file->f_path.mnt->mnt_sb->s_root);
                        mutex_lock(&root->d_inode->i_mutex);

                        while (!list_empty(&entries))
                                kill_node(list_entry(entries.next, Node, list));

                        mutex_unlock(&root->d_inode->i_mutex);
                        dput(root);
                default: return res;
        }
        return count;
}

static const struct file_operations bm_status_operations = {
        .read           = bm_status_read,
        .write          = bm_status_write,
};

/* Superblock handling */

static const struct super_operations s_ops = {
        .statfs         = simple_statfs,
        .clear_inode    = bm_clear_inode,
};

static int bm_fill_super(struct super_block * sb, void * data, int silent)
{
        static struct tree_descr bm_files[] = {
                [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
                [3] = {"register", &bm_register_operations, S_IWUSR},
                /* last one */ {""}
        };
        int err = simple_fill_super(sb, 0x42494e4d, bm_files);
        if (!err)
                sb->s_op = &s_ops;
        return err;
}

static int bm_get_sb(struct file_system_type *fs_type,
        int flags, const char *dev_name, void *data, struct vfsmount *mnt)
{
        return get_sb_single(fs_type, flags, data, bm_fill_super, mnt);
}

static struct linux_binfmt misc_format = {
        .module = THIS_MODULE,
        .load_binary = load_misc_binary,
};

static struct file_system_type bm_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "binfmt_misc",
        .get_sb         = bm_get_sb,
        .kill_sb        = kill_litter_super,
};

static int __init init_misc_binfmt(void)
{
        int err = register_filesystem(&bm_fs_type);
        if (!err) {
                err = register_binfmt(&misc_format);
                if (err)
                        unregister_filesystem(&bm_fs_type);
        }
        return err;
}

static void __exit exit_misc_binfmt(void)
{
        unregister_binfmt(&misc_format);
        unregister_filesystem(&bm_fs_type);
}

core_initcall(init_misc_binfmt);
module_exit(exit_misc_binfmt);
MODULE_LICENSE("GPL");