/*
 *  linux/fs/open.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <linux/string.h>
#include <linux/mm.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/fsnotify.h>
#include <linux/module.h>
#include <linux/tty.h>
#include <linux/namei.h>
#include <linux/backing-dev.h>
#include <linux/capability.h>
#include <linux/securebits.h>
#include <linux/security.h>
#include <linux/mount.h>
#include <linux/fcntl.h>
#include <linux/slab.h>
#include <asm/uaccess.h>
#include <linux/fs.h>
#include <linux/personality.h>
#include <linux/pagemap.h>
#include <linux/syscalls.h>
#include <linux/rcupdate.h>
#include <linux/audit.h>
#include <linux/falloc.h>
#include <linux/fs_struct.h>
#include <linux/ima.h>
#include <linux/dnotify.h>

#include "internal.h"

int do_truncate(struct dentry *dentry, loff_t length, unsigned int time_attrs,
        struct file *filp)
{
        int ret;
        struct iattr newattrs;

        /* Not pretty: "inode->i_size" shouldn't really be signed. But it is. */
        if (length < 0)
                return -EINVAL;

        newattrs.ia_size = length;
        newattrs.ia_valid = ATTR_SIZE | time_attrs;
        if (filp) {
                newattrs.ia_file = filp;
                newattrs.ia_valid |= ATTR_FILE;
        }

        /* Remove suid/sgid on truncate too */
        ret = should_remove_suid(dentry);
        if (ret)
                newattrs.ia_valid |= ret | ATTR_FORCE;

        mutex_lock(&dentry->d_inode->i_mutex);
        ret = notify_change(dentry, &newattrs);
        mutex_unlock(&dentry->d_inode->i_mutex);
        return ret;
}

static long do_sys_truncate(const char __user *pathname, loff_t length)
{
        struct path path;
        struct inode *inode;
        int error;

        error = -EINVAL;
        if (length < 0) /* sorry, but loff_t says... */
                goto out;

        error = user_path(pathname, &path);
        if (error)
                goto out;
        inode = path.dentry->d_inode;

        /* For directories it's -EISDIR, for other non-regulars - -EINVAL */
        error = -EISDIR;
        if (S_ISDIR(inode->i_mode))
                goto dput_and_out;

        error = -EINVAL;
        if (!S_ISREG(inode->i_mode))
                goto dput_and_out;

        error = mnt_want_write(path.mnt);
        if (error)
                goto dput_and_out;

        error = inode_permission(inode, MAY_WRITE);
        if (error)
                goto mnt_drop_write_and_out;

        error = -EPERM;
        if (IS_APPEND(inode))
                goto mnt_drop_write_and_out;

        error = get_write_access(inode);
        if (error)
                goto mnt_drop_write_and_out;

        /*
         * Make sure that there are no leases.  get_write_access() protects
         * against the truncate racing with a lease-granting setlease().
         */
        error = break_lease(inode, O_WRONLY);
        if (error)
                goto put_write_and_out;

        error = locks_verify_truncate(inode, NULL, length);
        if (!error)
                error = security_path_truncate(&path);
        if (!error)
                error = do_truncate(path.dentry, length, 0, NULL);

put_write_and_out:
        put_write_access(inode);
mnt_drop_write_and_out:
        mnt_drop_write(path.mnt);
dput_and_out:
        path_put(&path);
out:
        return error;
}

SYSCALL_DEFINE2(truncate, const char __user *, path, long, length)
{
        return do_sys_truncate(path, length);
}

static long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
{
        struct inode * inode;
        struct dentry *dentry;
        struct file * file;
        int error;

        error = -EINVAL;
        if (length < 0)
                goto out;
        error = -EBADF;
        file = fget(fd);
        if (!file)
                goto out;

        /* explicitly opened as large or we are on 64-bit box */
        if (file->f_flags & O_LARGEFILE)
                small = 0;

        dentry = file->f_path.dentry;
        inode = dentry->d_inode;
        error = -EINVAL;
        if (!S_ISREG(inode->i_mode) || !(file->f_mode & FMODE_WRITE))
                goto out_putf;

        error = -EINVAL;
        /* Cannot ftruncate over 2^31 bytes without large file support */
        if (small && length > MAX_NON_LFS)
                goto out_putf;

        error = -EPERM;
        if (IS_APPEND(inode))
                goto out_putf;

        error = locks_verify_truncate(inode, file, length);
        if (!error)
                error = security_path_truncate(&file->f_path);
        if (!error)
                error = do_truncate(dentry, length, ATTR_MTIME|ATTR_CTIME, file);
out_putf:
        fput(file);
out:
        return error;
}

SYSCALL_DEFINE2(ftruncate, unsigned int, fd, unsigned long, length)
{
        long ret = do_sys_ftruncate(fd, length, 1);
        /* avoid REGPARM breakage on x86: */
        asmlinkage_protect(2, ret, fd, length);
        return ret;
}

/* LFS versions of truncate are only needed on 32 bit machines */
#if BITS_PER_LONG == 32
SYSCALL_DEFINE(truncate64)(const char __user * path, loff_t length)
{
        return do_sys_truncate(path, length);
}
#ifdef CONFIG_HAVE_SYSCALL_WRAPPERS
asmlinkage long SyS_truncate64(long path, loff_t length)
{
        return SYSC_truncate64((const char __user *) path, length);
}
SYSCALL_ALIAS(sys_truncate64, SyS_truncate64);
#endif

SYSCALL_DEFINE(ftruncate64)(unsigned int fd, loff_t length)
{
        long ret = do_sys_ftruncate(fd, length, 0);
        /* avoid REGPARM breakage on x86: */
        asmlinkage_protect(2, ret, fd, length);
        return ret;
}
#ifdef CONFIG_HAVE_SYSCALL_WRAPPERS
asmlinkage long SyS_ftruncate64(long fd, loff_t length)
{
        return SYSC_ftruncate64((unsigned int) fd, length);
}
SYSCALL_ALIAS(sys_ftruncate64, SyS_ftruncate64);
#endif
#endif /* BITS_PER_LONG == 32 */


int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
{
        struct inode *inode = file->f_path.dentry->d_inode;
        long ret;

        if (offset < 0 || len <= 0)
                return -EINVAL;

        /* Return error if mode is not supported */
        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
                return -EOPNOTSUPP;

        /* Punch hole must have keep size set */
        if ((mode & FALLOC_FL_PUNCH_HOLE) &&
            !(mode & FALLOC_FL_KEEP_SIZE))
                return -EOPNOTSUPP;

        if (!(file->f_mode & FMODE_WRITE))
                return -EBADF;

        /* It's not possible punch hole on append only file */
        if (mode & FALLOC_FL_PUNCH_HOLE && IS_APPEND(inode))
                return -EPERM;

        if (IS_IMMUTABLE(inode))
                return -EPERM;

        /*
         * Revalidate the write permissions, in case security policy has
         * changed since the files were opened.
         */
        ret = security_file_permission(file, MAY_WRITE);
        if (ret)
                return ret;

        if (S_ISFIFO(inode->i_mode))
                return -ESPIPE;

        /*
         * Let individual file system decide if it supports preallocation
         * for directories or not.
         */
        if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
                return -ENODEV;

        /* Check for wrap through zero too */
        if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0))
                return -EFBIG;

        if (!file->f_op->fallocate)
                return -EOPNOTSUPP;

        return file->f_op->fallocate(file, mode, offset, len);
}

SYSCALL_DEFINE(fallocate)(int fd, int mode, loff_t offset, loff_t len)
{
        struct file *file;
        int error = -EBADF;

        file = fget(fd);
        if (file) {
                error = do_fallocate(file, mode, offset, len);
                fput(file);
        }

        return error;
}

#ifdef CONFIG_HAVE_SYSCALL_WRAPPERS
asmlinkage long SyS_fallocate(long fd, long mode, loff_t offset, loff_t len)
{
        return SYSC_fallocate((int)fd, (int)mode, offset, len);
}
SYSCALL_ALIAS(sys_fallocate, SyS_fallocate);
#endif

/*
 * access() needs to use the real uid/gid, not the effective uid/gid.
 * We do this by temporarily clearing all FS-related capabilities and
 * switching the fsuid/fsgid around to the real ones.
 */
SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
{
        const struct cred *old_cred;
        struct cred *override_cred;
        struct path path;
        struct inode *inode;
        int res;

        if (mode & ~S_IRWXO)    /* where's F_OK, X_OK, W_OK, R_OK? */
                return -EINVAL;

        override_cred = prepare_creds();
        if (!override_cred)
                return -ENOMEM;

        override_cred->fsuid = override_cred->uid;
        override_cred->fsgid = override_cred->gid;

        if (!issecure(SECURE_NO_SETUID_FIXUP)) {
                /* Clear the capabilities if we switch to a non-root user */
                kuid_t root_uid = make_kuid(override_cred->user_ns, 0);
                if (!uid_eq(override_cred->uid, root_uid))
                        cap_clear(override_cred->cap_effective);
                else
                        override_cred->cap_effective =
                                override_cred->cap_permitted;
        }

        old_cred = override_creds(override_cred);

        res = user_path_at(dfd, filename, LOOKUP_FOLLOW, &path);
        if (res)
                goto out;

        inode = path.dentry->d_inode;

        if ((mode & MAY_EXEC) && S_ISREG(inode->i_mode)) {
                /*
                 * MAY_EXEC on regular files is denied if the fs is mounted
                 * with the "noexec" flag.
                 */
                res = -EACCES;
                if (path.mnt->mnt_flags & MNT_NOEXEC)
                        goto out_path_release;
        }

        res = inode_permission(inode, mode | MAY_ACCESS);
        /* SuS v2 requires we report a read only fs too */
        if (res || !(mode & S_IWOTH) || special_file(inode->i_mode))
                goto out_path_release;
        /*
         * This is a rare case where using __mnt_is_readonly()
         * is OK without a mnt_want/drop_write() pair.  Since
         * no actual write to the fs is performed here, we do
         * not need to telegraph to that to anyone.
         *
         * By doing this, we accept that this access is
         * inherently racy and know that the fs may change
         * state before we even see this result.
         */
        if (__mnt_is_readonly(path.mnt))
                res = -EROFS;

out_path_release:
        path_put(&path);
out:
        revert_creds(old_cred);
        put_cred(override_cred);
        return res;
}

SYSCALL_DEFINE2(access, const char __user *, filename, int, mode)
{
        return sys_faccessat(AT_FDCWD, filename, mode);
}

SYSCALL_DEFINE1(chdir, const char __user *, filename)
{
        struct path path;
        int error;

        error = user_path_dir(filename, &path);
        if (error)
                goto out;

        error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);
        if (error)
                goto dput_and_out;

        set_fs_pwd(current->fs, &path);

dput_and_out:
        path_put(&path);
out:
        return error;
}

SYSCALL_DEFINE1(fchdir, unsigned int, fd)
{
        struct file *file;
        struct inode *inode;
        int error, fput_needed;

        error = -EBADF;
        file = fget_raw_light(fd, &fput_needed);
        if (!file)
                goto out;

        inode = file->f_path.dentry->d_inode;

        error = -ENOTDIR;
        if (!S_ISDIR(inode->i_mode))
                goto out_putf;

        error = inode_permission(inode, MAY_EXEC | MAY_CHDIR);
        if (!error)
                set_fs_pwd(current->fs, &file->f_path);
out_putf:
        fput_light(file, fput_needed);
out:
        return error;
}

SYSCALL_DEFINE1(chroot, const char __user *, filename)
{
        struct path path;
        int error;

        error = user_path_dir(filename, &path);
        if (error)
                goto out;

        error = inode_permission(path.dentry->d_inode, MAY_EXEC | MAY_CHDIR);
        if (error)
                goto dput_and_out;

        error = -EPERM;
        if (!capable(CAP_SYS_CHROOT))
                goto dput_and_out;
        error = security_path_chroot(&path);
        if (error)
                goto dput_and_out;

        set_fs_root(current->fs, &path);
        error = 0;
dput_and_out:
        path_put(&path);
out:
        return error;
}

static int chmod_common(struct path *path, umode_t mode)
{
        struct inode *inode = path->dentry->d_inode;
        struct iattr newattrs;
        int error;

        error = mnt_want_write(path->mnt);
        if (error)
                return error;
        mutex_lock(&inode->i_mutex);
        error = security_path_chmod(path, mode);
        if (error)
                goto out_unlock;
        newattrs.ia_mode = (mode & S_IALLUGO) | (inode->i_mode & ~S_IALLUGO);
        newattrs.ia_valid = ATTR_MODE | ATTR_CTIME;
        error = notify_change(path->dentry, &newattrs);
out_unlock:
        mutex_unlock(&inode->i_mutex);
        mnt_drop_write(path->mnt);
        return error;
}

SYSCALL_DEFINE2(fchmod, unsigned int, fd, umode_t, mode)
{
        struct file * file;
        int err = -EBADF;

        file = fget(fd);
        if (file) {
                audit_inode(NULL, file->f_path.dentry);
                err = chmod_common(&file->f_path, mode);
                fput(file);
        }
        return err;
}

SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, umode_t, mode)
{
        struct path path;
        int error;

        error = user_path_at(dfd, filename, LOOKUP_FOLLOW, &path);
        if (!error) {
                error = chmod_common(&path, mode);
                path_put(&path);
        }
        return error;
}

SYSCALL_DEFINE2(chmod, const char __user *, filename, umode_t, mode)
{
        return sys_fchmodat(AT_FDCWD, filename, mode);
}

static int chown_common(struct path *path, uid_t user, gid_t group)
{
        struct inode *inode = path->dentry->d_inode;
        int error;
        struct iattr newattrs;
        kuid_t uid;
        kgid_t gid;

        uid = make_kuid(current_user_ns(), user);
        gid = make_kgid(current_user_ns(), group);

        newattrs.ia_valid =  ATTR_CTIME;
        if (user != (uid_t) -1) {
                if (!uid_valid(uid))
                        return -EINVAL;
                newattrs.ia_valid |= ATTR_UID;
                newattrs.ia_uid = uid;
        }
        if (group != (gid_t) -1) {
                if (!gid_valid(gid))
                        return -EINVAL;
                newattrs.ia_valid |= ATTR_GID;
                newattrs.ia_gid = gid;
        }
        if (!S_ISDIR(inode->i_mode))
                newattrs.ia_valid |=
                        ATTR_KILL_SUID | ATTR_KILL_SGID | ATTR_KILL_PRIV;
        mutex_lock(&inode->i_mutex);
        error = security_path_chown(path, user, group);
        if (!error)
                error = notify_change(path->dentry, &newattrs);
        mutex_unlock(&inode->i_mutex);

        return error;
}

SYSCALL_DEFINE3(chown, const char __user *, filename, uid_t, user, gid_t, group)
{
        struct path path;
        int error;

        error = user_path(filename, &path);
        if (error)
                goto out;
        error = mnt_want_write(path.mnt);
        if (error)
                goto out_release;
        error = chown_common(&path, user, group);
        mnt_drop_write(path.mnt);
out_release:
        path_put(&path);
out:
        return error;
}

SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,
                gid_t, group, int, flag)
{
        struct path path;
        int error = -EINVAL;
        int lookup_flags;

        if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
                goto out;

        lookup_flags = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
        if (flag & AT_EMPTY_PATH)
                lookup_flags |= LOOKUP_EMPTY;
        error = user_path_at(dfd, filename, lookup_flags, &path);
        if (error)
                goto out;
        error = mnt_want_write(path.mnt);
        if (error)
                goto out_release;
        error = chown_common(&path, user, group);
        mnt_drop_write(path.mnt);
out_release:
        path_put(&path);
out:
        return error;
}

SYSCALL_DEFINE3(lchown, const char __user *, filename, uid_t, user, gid_t, group)
{
        struct path path;
        int error;

        error = user_lpath(filename, &path);
        if (error)
                goto out;
        error = mnt_want_write(path.mnt);
        if (error)
                goto out_release;
        error = chown_common(&path, user, group);
        mnt_drop_write(path.mnt);
out_release:
        path_put(&path);
out:
        return error;
}

SYSCALL_DEFINE3(fchown, unsigned int, fd, uid_t, user, gid_t, group)
{
        struct file * file;
        int error = -EBADF;
        struct dentry * dentry;

        file = fget(fd);
        if (!file)
                goto out;

        error = mnt_want_write_file(file);
        if (error)
                goto out_fput;
        dentry = file->f_path.dentry;
        audit_inode(NULL, dentry);
        error = chown_common(&file->f_path, user, group);
        mnt_drop_write_file(file);
out_fput:
        fput(file);
out:
        return error;
}

/*
 * You have to be very careful that these write
 * counts get cleaned up in error cases and
 * upon __fput().  This should probably never
 * be called outside of __dentry_open().
 */
static inline int __get_file_write_access(struct inode *inode,
                                          struct vfsmount *mnt)
{
        int error;
        error = get_write_access(inode);
        if (error)
                return error;
        /*
         * Do not take mount writer counts on
         * special files since no writes to
         * the mount itself will occur.
         */
        if (!special_file(inode->i_mode)) {
                /*
                 * Balanced in __fput()
                 */
                error = mnt_want_write(mnt);
                if (error)
                        put_write_access(inode);
        }
        return error;
}

int open_check_o_direct(struct file *f)
{
        /* NB: we're sure to have correct a_ops only after f_op->open */
        if (f->f_flags & O_DIRECT) {
                if (!f->f_mapping->a_ops ||
                    ((!f->f_mapping->a_ops->direct_IO) &&
                    (!f->f_mapping->a_ops->get_xip_mem))) {
                        return -EINVAL;
                }
        }
        return 0;
}

static struct file *do_dentry_open(struct dentry *dentry, struct vfsmount *mnt,
                                   struct file *f,
                                   int (*open)(struct inode *, struct file *),
                                   const struct cred *cred)
{
        static const struct file_operations empty_fops = {};
        struct inode *inode;
        int error;

        f->f_mode = OPEN_FMODE(f->f_flags) | FMODE_LSEEK |
                                FMODE_PREAD | FMODE_PWRITE;

        if (unlikely(f->f_flags & O_PATH))
                f->f_mode = FMODE_PATH;

        inode = dentry->d_inode;
        if (f->f_mode & FMODE_WRITE) {
                error = __get_file_write_access(inode, mnt);
                if (error)
                        goto cleanup_file;
                if (!special_file(inode->i_mode))
                        file_take_write(f);
        }

        f->f_mapping = inode->i_mapping;
        f->f_path.dentry = dentry;
        f->f_path.mnt = mnt;
        f->f_pos = 0;
        file_sb_list_add(f, inode->i_sb);

        if (unlikely(f->f_mode & FMODE_PATH)) {
                f->f_op = &empty_fops;
                return f;
        }

        f->f_op = fops_get(inode->i_fop);

        error = security_file_open(f, cred);
        if (error)
                goto cleanup_all;

        error = break_lease(inode, f->f_flags);
        if (error)
                goto cleanup_all;

        if (!open && f->f_op)
                open = f->f_op->open;
        if (open) {
                error = open(inode, f);
                if (error)
                        goto cleanup_all;
        }
        if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
                i_readcount_inc(inode);

        f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);

        file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping);

        return f;

cleanup_all:
        fops_put(f->f_op);
        if (f->f_mode & FMODE_WRITE) {
                put_write_access(inode);
                if (!special_file(inode->i_mode)) {
                        /*
                         * We don't consider this a real
                         * mnt_want/drop_write() pair
                         * because it all happenend right
                         * here, so just reset the state.
                         */
                        file_reset_write(f);
                        mnt_drop_write(mnt);
                }
        }
        file_sb_list_del(f);
        f->f_path.dentry = NULL;
        f->f_path.mnt = NULL;
cleanup_file:
        dput(dentry);
        mntput(mnt);
        return ERR_PTR(error);
}

static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt,
                                struct file *f,
                                int (*open)(struct inode *, struct file *),
                                const struct cred *cred)
{
        struct file *res = do_dentry_open(dentry, mnt, f, open, cred);
        if (!IS_ERR(res)) {
                int error = open_check_o_direct(f);
                if (error) {
                        fput(res);
                        res = ERR_PTR(error);
                }
        } else {
                put_filp(f);
        }
        return res;
}

/**
 * lookup_instantiate_filp - instantiates the open intent filp
 * @nd: pointer to nameidata
 * @dentry: pointer to dentry
 * @open: open callback
 *
 * Helper for filesystems that want to use lookup open intents and pass back
 * a fully instantiated struct file to the caller.
 * This function is meant to be called from within a filesystem's
 * lookup method.
 * Beware of calling it for non-regular files! Those ->open methods might block
 * (e.g. in fifo_open), leaving you with parent locked (and in case of fifo,
 * leading to a deadlock, as nobody can open that fifo anymore, because
 * another process to open fifo will block on locked parent when doing lookup).
 * Note that in case of error, nd->intent.open.file is destroyed, but the
 * path information remains valid.
 * If the open callback is set to NULL, then the standard f_op->open()
 * filesystem callback is substituted.
 */
struct file *lookup_instantiate_filp(struct nameidata *nd, struct dentry *dentry,
                int (*open)(struct inode *, struct file *))
{
        const struct cred *cred = current_cred();

        if (IS_ERR(nd->intent.open.file))
                goto out;
        if (IS_ERR(dentry))
                goto out_err;
        nd->intent.open.file = __dentry_open(dget(dentry), mntget(nd->path.mnt),
                                             nd->intent.open.file,
                                             open, cred);
out:
        return nd->intent.open.file;
out_err:
        release_open_intent(nd);
        nd->intent.open.file = ERR_CAST(dentry);
        goto out;
}
EXPORT_SYMBOL_GPL(lookup_instantiate_filp);

/**
 * nameidata_to_filp - convert a nameidata to an open filp.
 * @nd: pointer to nameidata
 * @flags: open flags
 *
 * Note that this function destroys the original nameidata
 */
struct file *nameidata_to_filp(struct nameidata *nd)
{
        const struct cred *cred = current_cred();
        struct file *filp;

        /* Pick up the filp from the open intent */
        filp = nd->intent.open.file;

        /* Has the filesystem initialised the file for us? */
        if (filp->f_path.dentry != NULL) {
                nd->intent.open.file = NULL;
        } else {
                struct file *res;

                path_get(&nd->path);
                res = do_dentry_open(nd->path.dentry, nd->path.mnt,
                                     filp, NULL, cred);
                if (!IS_ERR(res)) {
                        int error;

                        nd->intent.open.file = NULL;
                        BUG_ON(res != filp);

                        error = open_check_o_direct(filp);
                        if (error) {
                                fput(filp);
                                filp = ERR_PTR(error);
                        }
                } else {
                        /* Allow nd->intent.open.file to be recycled */
                        filp = res;
                }
        }
        return filp;
}

/*
 * dentry_open() will have done dput(dentry) and mntput(mnt) if it returns an
 * error.
 */
struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags,
                         const struct cred *cred)
{
        int error;
        struct file *f;

        validate_creds(cred);

        /* We must always pass in a valid mount pointer. */
        BUG_ON(!mnt);

        error = -ENFILE;
        f = get_empty_filp();
        if (f == NULL) {
                dput(dentry);
                mntput(mnt);
                return ERR_PTR(error);
        }

        f->f_flags = flags;
        return __dentry_open(dentry, mnt, f, NULL, cred);
}
EXPORT_SYMBOL(dentry_open);

static void __put_unused_fd(struct files_struct *files, unsigned int fd)
{
        struct fdtable *fdt = files_fdtable(files);
        __clear_open_fd(fd, fdt);
        if (fd < files->next_fd)
                files->next_fd = fd;
}

void put_unused_fd(unsigned int fd)
{
        struct files_struct *files = current->files;
        spin_lock(&files->file_lock);
        __put_unused_fd(files, fd);
        spin_unlock(&files->file_lock);
}

EXPORT_SYMBOL(put_unused_fd);

/*
 * Install a file pointer in the fd array.
 *
 * The VFS is full of places where we drop the files lock between
 * setting the open_fds bitmap and installing the file in the file
 * array.  At any such point, we are vulnerable to a dup2() race
 * installing a file in the array before us.  We need to detect this and
 * fput() the struct file we are about to overwrite in this case.
 *
 * It should never happen - if we allow dup2() do it, _really_ bad things
 * will follow.
 */

void fd_install(unsigned int fd, struct file *file)
{
        struct files_struct *files = current->files;
        struct fdtable *fdt;
        spin_lock(&files->file_lock);
        fdt = files_fdtable(files);
        BUG_ON(fdt->fd[fd] != NULL);
        rcu_assign_pointer(fdt->fd[fd], file);
        spin_unlock(&files->file_lock);
}

EXPORT_SYMBOL(fd_install);

static inline int build_open_flags(int flags, umode_t mode, struct open_flags *op)
{
        int lookup_flags = 0;
        int acc_mode;

        if (flags & O_CREAT)
                op->mode = (mode & S_IALLUGO) | S_IFREG;
        else
                op->mode = 0;

        /* Must never be set by userspace */
        flags &= ~FMODE_NONOTIFY;

        /*
         * O_SYNC is implemented as __O_SYNC|O_DSYNC.  As many places only
         * check for O_DSYNC if the need any syncing at all we enforce it's
         * always set instead of having to deal with possibly weird behaviour
         * for malicious applications setting only __O_SYNC.
         */
        if (flags & __O_SYNC)
                flags |= O_DSYNC;

        /*
         * If we have O_PATH in the open flag. Then we
         * cannot have anything other than the below set of flags
         */
        if (flags & O_PATH) {
                flags &= O_DIRECTORY | O_NOFOLLOW | O_PATH;
                acc_mode = 0;
        } else {
                acc_mode = MAY_OPEN | ACC_MODE(flags);
        }

        op->open_flag = flags;

        /* O_TRUNC implies we need access checks for write permissions */
        if (flags & O_TRUNC)
                acc_mode |= MAY_WRITE;

        /* Allow the LSM permission hook to distinguish append
           access from general write access. */
        if (flags & O_APPEND)
                acc_mode |= MAY_APPEND;

        op->acc_mode = acc_mode;

        op->intent = flags & O_PATH ? 0 : LOOKUP_OPEN;

        if (flags & O_CREAT) {
                op->intent |= LOOKUP_CREATE;
                if (flags & O_EXCL)
                        op->intent |= LOOKUP_EXCL;
        }

        if (flags & O_DIRECTORY)
                lookup_flags |= LOOKUP_DIRECTORY;
        if (!(flags & O_NOFOLLOW))
                lookup_flags |= LOOKUP_FOLLOW;
        return lookup_flags;
}

/**
 * filp_open - open file and return file pointer
 *
 * @filename:   path to open
 * @flags:      open flags as per the open(2) second argument
 * @mode:       mode for the new file if O_CREAT is set, else ignored
 *
 * This is the helper to open a file from kernelspace if you really
 * have to.  But in generally you should not do this, so please move
 * along, nothing to see here..
 */
struct file *filp_open(const char *filename, int flags, umode_t mode)

{
        struct open_flags op;
        int lookup = build_open_flags(flags, mode, &op);
        return do_filp_open(AT_FDCWD, filename, &op, lookup);
}
EXPORT_SYMBOL(filp_open);

struct file *file_open_root(struct dentry *dentry, struct vfsmount *mnt,
                            const char *filename, int flags)
{
        struct open_flags op;
        int lookup = build_open_flags(flags, 0, &op);
        if (flags & O_CREAT)
                return ERR_PTR(-EINVAL);
        if (!filename && (flags & O_DIRECTORY))
                if (!dentry->d_inode->i_op->lookup)
                        return ERR_PTR(-ENOTDIR);
        return do_file_open_root(dentry, mnt, filename, &op, lookup);
}
EXPORT_SYMBOL(file_open_root);

long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode)
{
        struct open_flags op;
        int lookup = build_open_flags(flags, mode, &op);
        char *tmp = getname(filename);
        int fd = PTR_ERR(tmp);

        if (!IS_ERR(tmp)) {
                fd = get_unused_fd_flags(flags);
                if (fd >= 0) {
                        struct file *f = do_filp_open(dfd, tmp, &op, lookup);
                        if (IS_ERR(f)) {
                                put_unused_fd(fd);
                                fd = PTR_ERR(f);
                        } else {
                                fsnotify_open(f);
                                fd_install(fd, f);
                        }
                }
                putname(tmp);
        }
        return fd;
}

SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t, mode)
{
        long ret;

        if (force_o_largefile())
                flags |= O_LARGEFILE;

        ret = do_sys_open(AT_FDCWD, filename, flags, mode);
        /* avoid REGPARM breakage on x86: */
        asmlinkage_protect(3, ret, filename, flags, mode);
        return ret;
}

SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags,
                umode_t, mode)
{
        long ret;

        if (force_o_largefile())
                flags |= O_LARGEFILE;

        ret = do_sys_open(dfd, filename, flags, mode);
        /* avoid REGPARM breakage on x86: */
        asmlinkage_protect(4, ret, dfd, filename, flags, mode);
        return ret;
}

#ifndef __alpha__

/*
 * For backward compatibility?  Maybe this should be moved
 * into arch/i386 instead?
 */
SYSCALL_DEFINE2(creat, const char __user *, pathname, umode_t, mode)
{
        return sys_open(pathname, O_CREAT | O_WRONLY | O_TRUNC, mode);
}

#endif

/*
 * "id" is the POSIX thread ID. We use the
 * files pointer for this..
 */
int filp_close(struct file *filp, fl_owner_t id)
{
        int retval = 0;

        if (!file_count(filp)) {
                printk(KERN_ERR "VFS: Close: file count is 0\n");
                return 0;
        }

        if (filp->f_op && filp->f_op->flush)
                retval = filp->f_op->flush(filp, id);

        if (likely(!(filp->f_mode & FMODE_PATH))) {
                dnotify_flush(filp, id);
                locks_remove_posix(filp, id);
        }
        fput(filp);
        return retval;
}

EXPORT_SYMBOL(filp_close);

/*
 * Careful here! We test whether the file pointer is NULL before
 * releasing the fd. This ensures that one clone task can't release
 * an fd while another clone is opening it.
 */
SYSCALL_DEFINE1(close, unsigned int, fd)
{
        struct file * filp;
        struct files_struct *files = current->files;
        struct fdtable *fdt;
        int retval;

        spin_lock(&files->file_lock);
        fdt = files_fdtable(files);
        if (fd >= fdt->max_fds)
                goto out_unlock;
        filp = fdt->fd[fd];
        if (!filp)
                goto out_unlock;
        rcu_assign_pointer(fdt->fd[fd], NULL);
        __clear_close_on_exec(fd, fdt);
        __put_unused_fd(files, fd);
        spin_unlock(&files->file_lock);
        retval = filp_close(filp, files);

        /* can't restart close syscall because file table entry was cleared */
        if (unlikely(retval == -ERESTARTSYS ||
                     retval == -ERESTARTNOINTR ||
                     retval == -ERESTARTNOHAND ||
                     retval == -ERESTART_RESTARTBLOCK))
                retval = -EINTR;

        return retval;

out_unlock:
        spin_unlock(&files->file_lock);
        return -EBADF;
}
EXPORT_SYMBOL(sys_close);

/*
 * This routine simulates a hangup on the tty, to arrange that users
 * are given clean terminals at login time.
 */
SYSCALL_DEFINE0(vhangup)
{
        if (capable(CAP_SYS_TTY_CONFIG)) {
                tty_vhangup_self();
                return 0;
        }
        return -EPERM;
}

/*
 * Called when an inode is about to be open.
 * We use this to disallow opening large files on 32bit systems if
 * the caller didn't specify O_LARGEFILE.  On 64bit systems we force
 * on this flag in sys_open.
 */
int generic_file_open(struct inode * inode, struct file * filp)
{
        if (!(filp->f_flags & O_LARGEFILE) && i_size_read(inode) > MAX_NON_LFS)
                return -EOVERFLOW;
        return 0;
}

EXPORT_SYMBOL(generic_file_open);

/*
 * This is used by subsystems that don't want seekable
 * file descriptors. The function is not supposed to ever fail, the only
 * reason it returns an 'int' and not 'void' is so that it can be plugged
 * directly into file_operations structure.
 */
int nonseekable_open(struct inode *inode, struct file *filp)
{
        filp->f_mode &= ~(FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE);
        return 0;
}

EXPORT_SYMBOL(nonseekable_open);