fs: get mnt_writers count for an open backing file's real path

[thirdparty/kernel/linux.git] / fs / open.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  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 <linux/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 <linux/compat.h>
#include <linux/mnt_idmapping.h>
#include <linux/filelock.h>

#include "internal.h"

int do_truncate(struct mnt_idmap *idmap, 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, and file capabilities on truncate too */
        ret = dentry_needs_remove_privs(idmap, dentry);
        if (ret < 0)
                return ret;
        if (ret)
                newattrs.ia_valid |= ret | ATTR_FORCE;

        inode_lock(dentry->d_inode);
        /* Note any delegations or leases have already been broken: */
        ret = notify_change(idmap, dentry, &newattrs, NULL);
        inode_unlock(dentry->d_inode);
        return ret;
}

long vfs_truncate(const struct path *path, loff_t length)
{
        struct mnt_idmap *idmap;
        struct inode *inode;
        long error;

        inode = path->dentry->d_inode;

        /* For directories it's -EISDIR, for other non-regulars - -EINVAL */
        if (S_ISDIR(inode->i_mode))
                return -EISDIR;
        if (!S_ISREG(inode->i_mode))
                return -EINVAL;

        error = mnt_want_write(path->mnt);
        if (error)
                goto out;

        idmap = mnt_idmap(path->mnt);
        error = inode_permission(idmap, 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 = security_path_truncate(path);
        if (!error)
                error = do_truncate(idmap, path->dentry, length, 0, NULL);

put_write_and_out:
        put_write_access(inode);
mnt_drop_write_and_out:
        mnt_drop_write(path->mnt);
out:
        return error;
}
EXPORT_SYMBOL_GPL(vfs_truncate);

long do_sys_truncate(const char __user *pathname, loff_t length)
{
        unsigned int lookup_flags = LOOKUP_FOLLOW;
        struct path path;
        int error;

        if (length < 0) /* sorry, but loff_t says... */
                return -EINVAL;

retry:
        error = user_path_at(AT_FDCWD, pathname, lookup_flags, &path);
        if (!error) {
                error = vfs_truncate(&path, length);
                path_put(&path);
        }
        if (retry_estale(error, lookup_flags)) {
                lookup_flags |= LOOKUP_REVAL;
                goto retry;
        }
        return error;
}

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

#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE2(truncate, const char __user *, path, compat_off_t, length)
{
        return do_sys_truncate(path, length);
}
#endif

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

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

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

        dentry = f.file->f_path.dentry;
        inode = dentry->d_inode;
        error = -EINVAL;
        if (!S_ISREG(inode->i_mode) || !(f.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;
        /* Check IS_APPEND on real upper inode */
        if (IS_APPEND(file_inode(f.file)))
                goto out_putf;
        sb_start_write(inode->i_sb);
        error = security_file_truncate(f.file);
        if (!error)
                error = do_truncate(file_mnt_idmap(f.file), dentry, length,
                                    ATTR_MTIME | ATTR_CTIME, f.file);
        sb_end_write(inode->i_sb);
out_putf:
        fdput(f);
out:
        return error;
}

SYSCALL_DEFINE2(ftruncate, unsigned int, fd, unsigned long, length)
{
        return do_sys_ftruncate(fd, length, 1);
}

#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE2(ftruncate, unsigned int, fd, compat_ulong_t, length)
{
        return do_sys_ftruncate(fd, length, 1);
}
#endif

/* LFS versions of truncate are only needed on 32 bit machines */
#if BITS_PER_LONG == 32
SYSCALL_DEFINE2(truncate64, const char __user *, path, loff_t, length)
{
        return do_sys_truncate(path, length);
}

SYSCALL_DEFINE2(ftruncate64, unsigned int, fd, loff_t, length)
{
        return do_sys_ftruncate(fd, length, 0);
}
#endif /* BITS_PER_LONG == 32 */

#if defined(CONFIG_COMPAT) && defined(__ARCH_WANT_COMPAT_TRUNCATE64)
COMPAT_SYSCALL_DEFINE3(truncate64, const char __user *, pathname,
                       compat_arg_u64_dual(length))
{
        return ksys_truncate(pathname, compat_arg_u64_glue(length));
}
#endif

#if defined(CONFIG_COMPAT) && defined(__ARCH_WANT_COMPAT_FTRUNCATE64)
COMPAT_SYSCALL_DEFINE3(ftruncate64, unsigned int, fd,
                       compat_arg_u64_dual(length))
{
        return ksys_ftruncate(fd, compat_arg_u64_glue(length));
}
#endif

int vfs_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
{
        struct inode *inode = file_inode(file);
        long ret;

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

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

        /* Punch hole and zero range are mutually exclusive */
        if ((mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE)) ==
            (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE))
                return -EOPNOTSUPP;

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

        /* Collapse range should only be used exclusively. */
        if ((mode & FALLOC_FL_COLLAPSE_RANGE) &&
            (mode & ~FALLOC_FL_COLLAPSE_RANGE))
                return -EINVAL;

        /* Insert range should only be used exclusively. */
        if ((mode & FALLOC_FL_INSERT_RANGE) &&
            (mode & ~FALLOC_FL_INSERT_RANGE))
                return -EINVAL;

        /* Unshare range should only be used with allocate mode. */
        if ((mode & FALLOC_FL_UNSHARE_RANGE) &&
            (mode & ~(FALLOC_FL_UNSHARE_RANGE | FALLOC_FL_KEEP_SIZE)))
                return -EINVAL;

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

        /*
         * We can only allow pure fallocate on append only files
         */
        if ((mode & ~FALLOC_FL_KEEP_SIZE) && IS_APPEND(inode))
                return -EPERM;

        if (IS_IMMUTABLE(inode))
                return -EPERM;

        /*
         * We cannot allow any fallocate operation on an active swapfile
         */
        if (IS_SWAPFILE(inode))
                return -ETXTBSY;

        /*
         * 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;

        if (S_ISDIR(inode->i_mode))
                return -EISDIR;

        if (!S_ISREG(inode->i_mode) && !S_ISBLK(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;

        file_start_write(file);
        ret = file->f_op->fallocate(file, mode, offset, len);

        /*
         * Create inotify and fanotify events.
         *
         * To keep the logic simple always create events if fallocate succeeds.
         * This implies that events are even created if the file size remains
         * unchanged, e.g. when using flag FALLOC_FL_KEEP_SIZE.
         */
        if (ret == 0)
                fsnotify_modify(file);

        file_end_write(file);
        return ret;
}
EXPORT_SYMBOL_GPL(vfs_fallocate);

int ksys_fallocate(int fd, int mode, loff_t offset, loff_t len)
{
        struct fd f = fdget(fd);
        int error = -EBADF;

        if (f.file) {
                error = vfs_fallocate(f.file, mode, offset, len);
                fdput(f);
        }
        return error;
}

SYSCALL_DEFINE4(fallocate, int, fd, int, mode, loff_t, offset, loff_t, len)
{
        return ksys_fallocate(fd, mode, offset, len);
}

#if defined(CONFIG_COMPAT) && defined(__ARCH_WANT_COMPAT_FALLOCATE)
COMPAT_SYSCALL_DEFINE6(fallocate, int, fd, int, mode, compat_arg_u64_dual(offset),
                       compat_arg_u64_dual(len))
{
        return ksys_fallocate(fd, mode, compat_arg_u64_glue(offset),
                              compat_arg_u64_glue(len));
}
#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.
 *
 * Creating new credentials is expensive, so we try to skip doing it,
 * which we can if the result would match what we already got.
 */
static bool access_need_override_creds(int flags)
{
        const struct cred *cred;

        if (flags & AT_EACCESS)
                return false;

        cred = current_cred();
        if (!uid_eq(cred->fsuid, cred->uid) ||
            !gid_eq(cred->fsgid, cred->gid))
                return true;

        if (!issecure(SECURE_NO_SETUID_FIXUP)) {
                kuid_t root_uid = make_kuid(cred->user_ns, 0);
                if (!uid_eq(cred->uid, root_uid)) {
                        if (!cap_isclear(cred->cap_effective))
                                return true;
                } else {
                        if (!cap_isidentical(cred->cap_effective,
                            cred->cap_permitted))
                                return true;
                }
        }

        return false;
}

static const struct cred *access_override_creds(void)
{
        const struct cred *old_cred;
        struct cred *override_cred;

        override_cred = prepare_creds();
        if (!override_cred)
                return NULL;

        /*
         * XXX access_need_override_creds performs checks in hopes of skipping
         * this work. Make sure it stays in sync if making any changes in this
         * routine.
         */

        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;
        }

        /*
         * The new set of credentials can *only* be used in
         * task-synchronous circumstances, and does not need
         * RCU freeing, unless somebody then takes a separate
         * reference to it.
         *
         * NOTE! This is _only_ true because this credential
         * is used purely for override_creds() that installs
         * it as the subjective cred. Other threads will be
         * accessing ->real_cred, not the subjective cred.
         *
         * If somebody _does_ make a copy of this (using the
         * 'get_current_cred()' function), that will clear the
         * non_rcu field, because now that other user may be
         * expecting RCU freeing. But normal thread-synchronous
         * cred accesses will keep things non-RCY.
         */
        override_cred->non_rcu = 1;

        old_cred = override_creds(override_cred);

        /* override_cred() gets its own ref */
        put_cred(override_cred);

        return old_cred;
}

static long do_faccessat(int dfd, const char __user *filename, int mode, int flags)
{
        struct path path;
        struct inode *inode;
        int res;
        unsigned int lookup_flags = LOOKUP_FOLLOW;
        const struct cred *old_cred = NULL;

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

        if (flags & ~(AT_EACCESS | AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH))
                return -EINVAL;

        if (flags & AT_SYMLINK_NOFOLLOW)
                lookup_flags &= ~LOOKUP_FOLLOW;
        if (flags & AT_EMPTY_PATH)
                lookup_flags |= LOOKUP_EMPTY;

        if (access_need_override_creds(flags)) {
                old_cred = access_override_creds();
                if (!old_cred)
                        return -ENOMEM;
        }

retry:
        res = user_path_at(dfd, filename, lookup_flags, &path);
        if (res)
                goto out;

        inode = d_backing_inode(path.dentry);

        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_noexec(&path))
                        goto out_path_release;
        }

        res = inode_permission(mnt_idmap(path.mnt), 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);
        if (retry_estale(res, lookup_flags)) {
                lookup_flags |= LOOKUP_REVAL;
                goto retry;
        }
out:
        if (old_cred)
                revert_creds(old_cred);

        return res;
}

SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
{
        return do_faccessat(dfd, filename, mode, 0);
}

SYSCALL_DEFINE4(faccessat2, int, dfd, const char __user *, filename, int, mode,
                int, flags)
{
        return do_faccessat(dfd, filename, mode, flags);
}

SYSCALL_DEFINE2(access, const char __user *, filename, int, mode)
{
        return do_faccessat(AT_FDCWD, filename, mode, 0);
}

SYSCALL_DEFINE1(chdir, const char __user *, filename)
{
        struct path path;
        int error;
        unsigned int lookup_flags = LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
retry:
        error = user_path_at(AT_FDCWD, filename, lookup_flags, &path);
        if (error)
                goto out;

        error = path_permission(&path, MAY_EXEC | MAY_CHDIR);
        if (error)
                goto dput_and_out;

        set_fs_pwd(current->fs, &path);

dput_and_out:
        path_put(&path);
        if (retry_estale(error, lookup_flags)) {
                lookup_flags |= LOOKUP_REVAL;
                goto retry;
        }
out:
        return error;
}

SYSCALL_DEFINE1(fchdir, unsigned int, fd)
{
        struct fd f = fdget_raw(fd);
        int error;

        error = -EBADF;
        if (!f.file)
                goto out;

        error = -ENOTDIR;
        if (!d_can_lookup(f.file->f_path.dentry))
                goto out_putf;

        error = file_permission(f.file, MAY_EXEC | MAY_CHDIR);
        if (!error)
                set_fs_pwd(current->fs, &f.file->f_path);
out_putf:
        fdput(f);
out:
        return error;
}

SYSCALL_DEFINE1(chroot, const char __user *, filename)
{
        struct path path;
        int error;
        unsigned int lookup_flags = LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
retry:
        error = user_path_at(AT_FDCWD, filename, lookup_flags, &path);
        if (error)
                goto out;

        error = path_permission(&path, MAY_EXEC | MAY_CHDIR);
        if (error)
                goto dput_and_out;

        error = -EPERM;
        if (!ns_capable(current_user_ns(), 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);
        if (retry_estale(error, lookup_flags)) {
                lookup_flags |= LOOKUP_REVAL;
                goto retry;
        }
out:
        return error;
}

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

        error = mnt_want_write(path->mnt);
        if (error)
                return error;
retry_deleg:
        inode_lock(inode);
        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(mnt_idmap(path->mnt), path->dentry,
                              &newattrs, &delegated_inode);
out_unlock:
        inode_unlock(inode);
        if (delegated_inode) {
                error = break_deleg_wait(&delegated_inode);
                if (!error)
                        goto retry_deleg;
        }
        mnt_drop_write(path->mnt);
        return error;
}

int vfs_fchmod(struct file *file, umode_t mode)
{
        audit_file(file);
        return chmod_common(&file->f_path, mode);
}

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

        if (f.file) {
                err = vfs_fchmod(f.file, mode);
                fdput(f);
        }
        return err;
}

static int do_fchmodat(int dfd, const char __user *filename, umode_t mode,
                       unsigned int flags)
{
        struct path path;
        int error;
        unsigned int lookup_flags;

        if (unlikely(flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)))
                return -EINVAL;

        lookup_flags = (flags & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
        if (flags & AT_EMPTY_PATH)
                lookup_flags |= LOOKUP_EMPTY;

retry:
        error = user_path_at(dfd, filename, lookup_flags, &path);
        if (!error) {
                error = chmod_common(&path, mode);
                path_put(&path);
                if (retry_estale(error, lookup_flags)) {
                        lookup_flags |= LOOKUP_REVAL;
                        goto retry;
                }
        }
        return error;
}

SYSCALL_DEFINE4(fchmodat2, int, dfd, const char __user *, filename,
                umode_t, mode, unsigned int, flags)
{
        return do_fchmodat(dfd, filename, mode, flags);
}

SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename,
                umode_t, mode)
{
        return do_fchmodat(dfd, filename, mode, 0);
}

SYSCALL_DEFINE2(chmod, const char __user *, filename, umode_t, mode)
{
        return do_fchmodat(AT_FDCWD, filename, mode, 0);
}

/*
 * Check whether @kuid is valid and if so generate and set vfsuid_t in
 * ia_vfsuid.
 *
 * Return: true if @kuid is valid, false if not.
 */
static inline bool setattr_vfsuid(struct iattr *attr, kuid_t kuid)
{
        if (!uid_valid(kuid))
                return false;
        attr->ia_valid |= ATTR_UID;
        attr->ia_vfsuid = VFSUIDT_INIT(kuid);
        return true;
}

/*
 * Check whether @kgid is valid and if so generate and set vfsgid_t in
 * ia_vfsgid.
 *
 * Return: true if @kgid is valid, false if not.
 */
static inline bool setattr_vfsgid(struct iattr *attr, kgid_t kgid)
{
        if (!gid_valid(kgid))
                return false;
        attr->ia_valid |= ATTR_GID;
        attr->ia_vfsgid = VFSGIDT_INIT(kgid);
        return true;
}

int chown_common(const struct path *path, uid_t user, gid_t group)
{
        struct mnt_idmap *idmap;
        struct user_namespace *fs_userns;
        struct inode *inode = path->dentry->d_inode;
        struct inode *delegated_inode = NULL;
        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);

        idmap = mnt_idmap(path->mnt);
        fs_userns = i_user_ns(inode);

retry_deleg:
        newattrs.ia_vfsuid = INVALID_VFSUID;
        newattrs.ia_vfsgid = INVALID_VFSGID;
        newattrs.ia_valid =  ATTR_CTIME;
        if ((user != (uid_t)-1) && !setattr_vfsuid(&newattrs, uid))
                return -EINVAL;
        if ((group != (gid_t)-1) && !setattr_vfsgid(&newattrs, gid))
                return -EINVAL;
        inode_lock(inode);
        if (!S_ISDIR(inode->i_mode))
                newattrs.ia_valid |= ATTR_KILL_SUID | ATTR_KILL_PRIV |
                                     setattr_should_drop_sgid(idmap, inode);
        /* Continue to send actual fs values, not the mount values. */
        error = security_path_chown(
                path,
                from_vfsuid(idmap, fs_userns, newattrs.ia_vfsuid),
                from_vfsgid(idmap, fs_userns, newattrs.ia_vfsgid));
        if (!error)
                error = notify_change(idmap, path->dentry, &newattrs,
                                      &delegated_inode);
        inode_unlock(inode);
        if (delegated_inode) {
                error = break_deleg_wait(&delegated_inode);
                if (!error)
                        goto retry_deleg;
        }
        return error;
}

int do_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;
retry:
        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);
        if (retry_estale(error, lookup_flags)) {
                lookup_flags |= LOOKUP_REVAL;
                goto retry;
        }
out:
        return error;
}

SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,
                gid_t, group, int, flag)
{
        return do_fchownat(dfd, filename, user, group, flag);
}

SYSCALL_DEFINE3(chown, const char __user *, filename, uid_t, user, gid_t, group)
{
        return do_fchownat(AT_FDCWD, filename, user, group, 0);
}

SYSCALL_DEFINE3(lchown, const char __user *, filename, uid_t, user, gid_t, group)
{
        return do_fchownat(AT_FDCWD, filename, user, group,
                           AT_SYMLINK_NOFOLLOW);
}

int vfs_fchown(struct file *file, uid_t user, gid_t group)
{
        int error;

        error = mnt_want_write_file(file);
        if (error)
                return error;
        audit_file(file);
        error = chown_common(&file->f_path, user, group);
        mnt_drop_write_file(file);
        return error;
}

int ksys_fchown(unsigned int fd, uid_t user, gid_t group)
{
        struct fd f = fdget(fd);
        int error = -EBADF;

        if (f.file) {
                error = vfs_fchown(f.file, user, group);
                fdput(f);
        }
        return error;
}

SYSCALL_DEFINE3(fchown, unsigned int, fd, uid_t, user, gid_t, group)
{
        return ksys_fchown(fd, user, group);
}

static inline int file_get_write_access(struct file *f)
{
        int error;

        error = get_write_access(f->f_inode);
        if (unlikely(error))
                return error;
        error = mnt_get_write_access(f->f_path.mnt);
        if (unlikely(error))
                goto cleanup_inode;
        if (unlikely(f->f_mode & FMODE_BACKING)) {
                error = mnt_get_write_access(backing_file_real_path(f)->mnt);
                if (unlikely(error))
                        goto cleanup_mnt;
        }
        return 0;

cleanup_mnt:
        mnt_put_write_access(f->f_path.mnt);
cleanup_inode:
        put_write_access(f->f_inode);
        return error;
}

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

        path_get(&f->f_path);
        f->f_inode = inode;
        f->f_mapping = inode->i_mapping;
        f->f_wb_err = filemap_sample_wb_err(f->f_mapping);
        f->f_sb_err = file_sample_sb_err(f);

        if (unlikely(f->f_flags & O_PATH)) {
                f->f_mode = FMODE_PATH | FMODE_OPENED;
                f->f_op = &empty_fops;
                return 0;
        }

        if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) {
                i_readcount_inc(inode);
        } else if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
                error = file_get_write_access(f);
                if (unlikely(error))
                        goto cleanup_file;
                f->f_mode |= FMODE_WRITER;
        }

        /* POSIX.1-2008/SUSv4 Section XSI 2.9.7 */
        if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode))
                f->f_mode |= FMODE_ATOMIC_POS;

        f->f_op = fops_get(inode->i_fop);
        if (WARN_ON(!f->f_op)) {
                error = -ENODEV;
                goto cleanup_all;
        }

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

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

        /* normally all 3 are set; ->open() can clear them if needed */
        f->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
        if (!open)
                open = f->f_op->open;
        if (open) {
                error = open(inode, f);
                if (error)
                        goto cleanup_all;
        }
        f->f_mode |= FMODE_OPENED;
        if ((f->f_mode & FMODE_READ) &&
             likely(f->f_op->read || f->f_op->read_iter))
                f->f_mode |= FMODE_CAN_READ;
        if ((f->f_mode & FMODE_WRITE) &&
             likely(f->f_op->write || f->f_op->write_iter))
                f->f_mode |= FMODE_CAN_WRITE;
        if ((f->f_mode & FMODE_LSEEK) && !f->f_op->llseek)
                f->f_mode &= ~FMODE_LSEEK;
        if (f->f_mapping->a_ops && f->f_mapping->a_ops->direct_IO)
                f->f_mode |= FMODE_CAN_ODIRECT;

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

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

        if ((f->f_flags & O_DIRECT) && !(f->f_mode & FMODE_CAN_ODIRECT))
                return -EINVAL;

        /*
         * XXX: Huge page cache doesn't support writing yet. Drop all page
         * cache for this file before processing writes.
         */
        if (f->f_mode & FMODE_WRITE) {
                /*
                 * Paired with smp_mb() in collapse_file() to ensure nr_thps
                 * is up to date and the update to i_writecount by
                 * get_write_access() is visible. Ensures subsequent insertion
                 * of THPs into the page cache will fail.
                 */
                smp_mb();
                if (filemap_nr_thps(inode->i_mapping)) {
                        struct address_space *mapping = inode->i_mapping;

                        filemap_invalidate_lock(inode->i_mapping);
                        /*
                         * unmap_mapping_range just need to be called once
                         * here, because the private pages is not need to be
                         * unmapped mapping (e.g. data segment of dynamic
                         * shared libraries here).
                         */
                        unmap_mapping_range(mapping, 0, 0, 0);
                        truncate_inode_pages(mapping, 0);
                        filemap_invalidate_unlock(inode->i_mapping);
                }
        }

        /*
         * Once we return a file with FMODE_OPENED, __fput() will call
         * fsnotify_close(), so we need fsnotify_open() here for symmetry.
         */
        fsnotify_open(f);
        return 0;

cleanup_all:
        if (WARN_ON_ONCE(error > 0))
                error = -EINVAL;
        fops_put(f->f_op);
        put_file_access(f);
cleanup_file:
        path_put(&f->f_path);
        f->f_path.mnt = NULL;
        f->f_path.dentry = NULL;
        f->f_inode = NULL;
        return error;
}

/**
 * finish_open - finish opening a file
 * @file: file pointer
 * @dentry: pointer to dentry
 * @open: open callback
 *
 * This can be used to finish opening a file passed to i_op->atomic_open().
 *
 * If the open callback is set to NULL, then the standard f_op->open()
 * filesystem callback is substituted.
 *
 * NB: the dentry reference is _not_ consumed.  If, for example, the dentry is
 * the return value of d_splice_alias(), then the caller needs to perform dput()
 * on it after finish_open().
 *
 * Returns zero on success or -errno if the open failed.
 */
int finish_open(struct file *file, struct dentry *dentry,
                int (*open)(struct inode *, struct file *))
{
        BUG_ON(file->f_mode & FMODE_OPENED); /* once it's opened, it's opened */

        file->f_path.dentry = dentry;
        return do_dentry_open(file, d_backing_inode(dentry), open);
}
EXPORT_SYMBOL(finish_open);

/**
 * finish_no_open - finish ->atomic_open() without opening the file
 *
 * @file: file pointer
 * @dentry: dentry or NULL (as returned from ->lookup())
 *
 * This can be used to set the result of a successful lookup in ->atomic_open().
 *
 * NB: unlike finish_open() this function does consume the dentry reference and
 * the caller need not dput() it.
 *
 * Returns "0" which must be the return value of ->atomic_open() after having
 * called this function.
 */
int finish_no_open(struct file *file, struct dentry *dentry)
{
        file->f_path.dentry = dentry;
        return 0;
}
EXPORT_SYMBOL(finish_no_open);

char *file_path(struct file *filp, char *buf, int buflen)
{
        return d_path(&filp->f_path, buf, buflen);
}
EXPORT_SYMBOL(file_path);

/**
 * vfs_open - open the file at the given path
 * @path: path to open
 * @file: newly allocated file with f_flag initialized
 */
int vfs_open(const struct path *path, struct file *file)
{
        file->f_path = *path;
        return do_dentry_open(file, d_backing_inode(path->dentry), NULL);
}

struct file *dentry_open(const struct path *path, 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(!path->mnt);

        f = alloc_empty_file(flags, cred);
        if (!IS_ERR(f)) {
                error = vfs_open(path, f);
                if (error) {
                        fput(f);
                        f = ERR_PTR(error);
                }
        }
        return f;
}
EXPORT_SYMBOL(dentry_open);

/**
 * dentry_create - Create and open a file
 * @path: path to create
 * @flags: O_ flags
 * @mode: mode bits for new file
 * @cred: credentials to use
 *
 * Caller must hold the parent directory's lock, and have prepared
 * a negative dentry, placed in @path->dentry, for the new file.
 *
 * Caller sets @path->mnt to the vfsmount of the filesystem where
 * the new file is to be created. The parent directory and the
 * negative dentry must reside on the same filesystem instance.
 *
 * On success, returns a "struct file *". Otherwise a ERR_PTR
 * is returned.
 */
struct file *dentry_create(const struct path *path, int flags, umode_t mode,
                           const struct cred *cred)
{
        struct file *f;
        int error;

        validate_creds(cred);
        f = alloc_empty_file(flags, cred);
        if (IS_ERR(f))
                return f;

        error = vfs_create(mnt_idmap(path->mnt),
                           d_inode(path->dentry->d_parent),
                           path->dentry, mode, true);
        if (!error)
                error = vfs_open(path, f);

        if (unlikely(error)) {
                fput(f);
                return ERR_PTR(error);
        }
        return f;
}
EXPORT_SYMBOL(dentry_create);

/**
 * kernel_file_open - open a file for kernel internal use
 * @path:       path of the file to open
 * @flags:      open flags
 * @inode:      the inode
 * @cred:       credentials for open
 *
 * Open a file for use by in-kernel consumers. The file is not accounted
 * against nr_files and must not be installed into the file descriptor
 * table.
 *
 * Return: Opened file on success, an error pointer on failure.
 */
struct file *kernel_file_open(const struct path *path, int flags,
                                struct inode *inode, const struct cred *cred)
{
        struct file *f;
        int error;

        f = alloc_empty_file_noaccount(flags, cred);
        if (IS_ERR(f))
                return f;

        f->f_path = *path;
        error = do_dentry_open(f, inode, NULL);
        if (error) {
                fput(f);
                f = ERR_PTR(error);
        }
        return f;
}
EXPORT_SYMBOL_GPL(kernel_file_open);

/**
 * backing_file_open - open a backing file for kernel internal use
 * @path:       path of the file to open
 * @flags:      open flags
 * @real_path:  path of the backing file
 * @cred:       credentials for open
 *
 * Open a backing file for a stackable filesystem (e.g., overlayfs).
 * @path may be on the stackable filesystem and backing inode on the
 * underlying filesystem. In this case, we want to be able to return
 * the @real_path of the backing inode. This is done by embedding the
 * returned file into a container structure that also stores the path of
 * the backing inode on the underlying filesystem, which can be
 * retrieved using backing_file_real_path().
 */
struct file *backing_file_open(const struct path *path, int flags,
                               const struct path *real_path,
                               const struct cred *cred)
{
        struct file *f;
        int error;

        f = alloc_empty_backing_file(flags, cred);
        if (IS_ERR(f))
                return f;

        f->f_path = *path;
        path_get(real_path);
        *backing_file_real_path(f) = *real_path;
        error = do_dentry_open(f, d_inode(real_path->dentry), NULL);
        if (error) {
                fput(f);
                f = ERR_PTR(error);
        }

        return f;
}
EXPORT_SYMBOL_GPL(backing_file_open);

#define WILL_CREATE(flags)      (flags & (O_CREAT | __O_TMPFILE))
#define O_PATH_FLAGS            (O_DIRECTORY | O_NOFOLLOW | O_PATH | O_CLOEXEC)

inline struct open_how build_open_how(int flags, umode_t mode)
{
        struct open_how how = {
                .flags = flags & VALID_OPEN_FLAGS,
                .mode = mode & S_IALLUGO,
        };

        /* O_PATH beats everything else. */
        if (how.flags & O_PATH)
                how.flags &= O_PATH_FLAGS;
        /* Modes should only be set for create-like flags. */
        if (!WILL_CREATE(how.flags))
                how.mode = 0;
        return how;
}

inline int build_open_flags(const struct open_how *how, struct open_flags *op)
{
        u64 flags = how->flags;
        u64 strip = __FMODE_NONOTIFY | O_CLOEXEC;
        int lookup_flags = 0;
        int acc_mode = ACC_MODE(flags);

        BUILD_BUG_ON_MSG(upper_32_bits(VALID_OPEN_FLAGS),
                         "struct open_flags doesn't yet handle flags > 32 bits");

        /*
         * Strip flags that either shouldn't be set by userspace like
         * FMODE_NONOTIFY or that aren't relevant in determining struct
         * open_flags like O_CLOEXEC.
         */
        flags &= ~strip;

        /*
         * Older syscalls implicitly clear all of the invalid flags or argument
         * values before calling build_open_flags(), but openat2(2) checks all
         * of its arguments.
         */
        if (flags & ~VALID_OPEN_FLAGS)
                return -EINVAL;
        if (how->resolve & ~VALID_RESOLVE_FLAGS)
                return -EINVAL;

        /* Scoping flags are mutually exclusive. */
        if ((how->resolve & RESOLVE_BENEATH) && (how->resolve & RESOLVE_IN_ROOT))
                return -EINVAL;

        /* Deal with the mode. */
        if (WILL_CREATE(flags)) {
                if (how->mode & ~S_IALLUGO)
                        return -EINVAL;
                op->mode = how->mode | S_IFREG;
        } else {
                if (how->mode != 0)
                        return -EINVAL;
                op->mode = 0;
        }

        /*
         * Block bugs where O_DIRECTORY | O_CREAT created regular files.
         * Note, that blocking O_DIRECTORY | O_CREAT here also protects
         * O_TMPFILE below which requires O_DIRECTORY being raised.
         */
        if ((flags & (O_DIRECTORY | O_CREAT)) == (O_DIRECTORY | O_CREAT))
                return -EINVAL;

        /* Now handle the creative implementation of O_TMPFILE. */
        if (flags & __O_TMPFILE) {
                /*
                 * In order to ensure programs get explicit errors when trying
                 * to use O_TMPFILE on old kernels we enforce that O_DIRECTORY
                 * is raised alongside __O_TMPFILE.
                 */
                if (!(flags & O_DIRECTORY))
                        return -EINVAL;
                if (!(acc_mode & MAY_WRITE))
                        return -EINVAL;
        }
        if (flags & O_PATH) {
                /* O_PATH only permits certain other flags to be set. */
                if (flags & ~O_PATH_FLAGS)
                        return -EINVAL;
                acc_mode = 0;
        }

        /*
         * 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;

        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;
                        flags |= O_NOFOLLOW;
                }
        }

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

        if (how->resolve & RESOLVE_NO_XDEV)
                lookup_flags |= LOOKUP_NO_XDEV;
        if (how->resolve & RESOLVE_NO_MAGICLINKS)
                lookup_flags |= LOOKUP_NO_MAGICLINKS;
        if (how->resolve & RESOLVE_NO_SYMLINKS)
                lookup_flags |= LOOKUP_NO_SYMLINKS;
        if (how->resolve & RESOLVE_BENEATH)
                lookup_flags |= LOOKUP_BENEATH;
        if (how->resolve & RESOLVE_IN_ROOT)
                lookup_flags |= LOOKUP_IN_ROOT;
        if (how->resolve & RESOLVE_CACHED) {
                /* Don't bother even trying for create/truncate/tmpfile open */
                if (flags & (O_TRUNC | O_CREAT | __O_TMPFILE))
                        return -EAGAIN;
                lookup_flags |= LOOKUP_CACHED;
        }

        op->lookup_flags = lookup_flags;
        return 0;
}

/**
 * file_open_name - open file and return file pointer
 *
 * @name:       struct filename containing 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 *file_open_name(struct filename *name, int flags, umode_t mode)
{
        struct open_flags op;
        struct open_how how = build_open_how(flags, mode);
        int err = build_open_flags(&how, &op);
        if (err)
                return ERR_PTR(err);
        return do_filp_open(AT_FDCWD, name, &op);
}

/**
 * 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 filename *name = getname_kernel(filename);
        struct file *file = ERR_CAST(name);
        
        if (!IS_ERR(name)) {
                file = file_open_name(name, flags, mode);
                putname(name);
        }
        return file;
}
EXPORT_SYMBOL(filp_open);

struct file *file_open_root(const struct path *root,
                            const char *filename, int flags, umode_t mode)
{
        struct open_flags op;
        struct open_how how = build_open_how(flags, mode);
        int err = build_open_flags(&how, &op);
        if (err)
                return ERR_PTR(err);
        return do_file_open_root(root, filename, &op);
}
EXPORT_SYMBOL(file_open_root);

static long do_sys_openat2(int dfd, const char __user *filename,
                           struct open_how *how)
{
        struct open_flags op;
        int fd = build_open_flags(how, &op);
        struct filename *tmp;

        if (fd)
                return fd;

        tmp = getname(filename);
        if (IS_ERR(tmp))
                return PTR_ERR(tmp);

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

long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode)
{
        struct open_how how = build_open_how(flags, mode);
        return do_sys_openat2(dfd, filename, &how);
}


SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t, mode)
{
        if (force_o_largefile())
                flags |= O_LARGEFILE;
        return do_sys_open(AT_FDCWD, filename, flags, mode);
}

SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags,
                umode_t, mode)
{
        if (force_o_largefile())
                flags |= O_LARGEFILE;
        return do_sys_open(dfd, filename, flags, mode);
}

SYSCALL_DEFINE4(openat2, int, dfd, const char __user *, filename,
                struct open_how __user *, how, size_t, usize)
{
        int err;
        struct open_how tmp;

        BUILD_BUG_ON(sizeof(struct open_how) < OPEN_HOW_SIZE_VER0);
        BUILD_BUG_ON(sizeof(struct open_how) != OPEN_HOW_SIZE_LATEST);

        if (unlikely(usize < OPEN_HOW_SIZE_VER0))
                return -EINVAL;

        err = copy_struct_from_user(&tmp, sizeof(tmp), how, usize);
        if (err)
                return err;

        audit_openat2_how(&tmp);

        /* O_LARGEFILE is only allowed for non-O_PATH. */
        if (!(tmp.flags & O_PATH) && force_o_largefile())
                tmp.flags |= O_LARGEFILE;

        return do_sys_openat2(dfd, filename, &tmp);
}

#ifdef CONFIG_COMPAT
/*
 * Exactly like sys_open(), except that it doesn't set the
 * O_LARGEFILE flag.
 */
COMPAT_SYSCALL_DEFINE3(open, const char __user *, filename, int, flags, umode_t, mode)
{
        return do_sys_open(AT_FDCWD, filename, flags, mode);
}

/*
 * Exactly like sys_openat(), except that it doesn't set the
 * O_LARGEFILE flag.
 */
COMPAT_SYSCALL_DEFINE4(openat, int, dfd, const char __user *, filename, int, flags, umode_t, mode)
{
        return do_sys_open(dfd, filename, flags, mode);
}
#endif

#ifndef __alpha__

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

        if (force_o_largefile())
                flags |= O_LARGEFILE;
        return do_sys_open(AT_FDCWD, pathname, flags, mode);
}
#endif

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

        if (CHECK_DATA_CORRUPTION(file_count(filp) == 0,
                        "VFS: Close: file count is 0 (f_op=%ps)",
                        filp->f_op)) {
                return 0;
        }

        if (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);
        }
        return retval;
}

int filp_close(struct file *filp, fl_owner_t id)
{
        int retval;

        retval = filp_flush(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)
{
        int retval;
        struct file *file;

        file = close_fd_get_file(fd);
        if (!file)
                return -EBADF;

        retval = filp_flush(file, current->files);

        /*
         * We're returning to user space. Don't bother
         * with any delayed fput() cases.
         */
        __fput_sync(file);

        /* 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;
}

/**
 * sys_close_range() - Close all file descriptors in a given range.
 *
 * @fd:     starting file descriptor to close
 * @max_fd: last file descriptor to close
 * @flags:  reserved for future extensions
 *
 * This closes a range of file descriptors. All file descriptors
 * from @fd up to and including @max_fd are closed.
 * Currently, errors to close a given file descriptor are ignored.
 */
SYSCALL_DEFINE3(close_range, unsigned int, fd, unsigned int, max_fd,
                unsigned int, flags)
{
        return __close_range(fd, max_fd, flags);
}

/*
 * 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);

/*
 * stream_open is used by subsystems that want stream-like file descriptors.
 * Such file descriptors are not seekable and don't have notion of position
 * (file.f_pos is always 0 and ppos passed to .read()/.write() is always NULL).
 * Contrary to file descriptors of other regular files, .read() and .write()
 * can run simultaneously.
 *
 * stream_open never fails and is marked to return int so that it could be
 * directly used as file_operations.open .
 */
int stream_open(struct inode *inode, struct file *filp)
{
        filp->f_mode &= ~(FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE | FMODE_ATOMIC_POS);
        filp->f_mode |= FMODE_STREAM;
        return 0;
}

EXPORT_SYMBOL(stream_open);