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    Subject[PATCH -V14 10/11] vfs: Support null pathname in faccessat
    Date
    This enables to use faccessat to get the access check details
    from a file descriptor pointing to the file. This can be used
    with open_by_handle syscall that returns a file descriptor.

    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    ---
    fs/open.c | 27 ++++++++++++++++++++-------
    1 files changed, 20 insertions(+), 7 deletions(-)

    diff --git a/fs/open.c b/fs/open.c
    index 43093af..90fb12f 100644
    --- a/fs/open.c
    +++ b/fs/open.c
    @@ -288,7 +288,8 @@ SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
    {
    const struct cred *old_cred;
    struct cred *override_cred;
    - struct path path;
    + struct file *file = NULL;
    + struct path path, *pp;
    struct inode *inode;
    int res;

    @@ -312,12 +313,21 @@ SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
    }

    old_cred = override_creds(override_cred);
    -
    - res = user_path_at(dfd, filename, LOOKUP_FOLLOW, &path);
    + if (filename == NULL && dfd != AT_FDCWD) {
    + file = fget(dfd);
    + if (file) {
    + pp = &file->f_path;
    + res = 0;
    + } else
    + res = -EBADF;
    + } else {
    + res = user_path_at(dfd, filename, LOOKUP_FOLLOW, &path);
    + pp = &path;
    + }
    if (res)
    goto out;

    - inode = path.dentry->d_inode;
    + inode = pp->dentry->d_inode;

    if ((mode & MAY_EXEC) && S_ISREG(inode->i_mode)) {
    /*
    @@ -325,7 +335,7 @@ SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
    * with the "noexec" flag.
    */
    res = -EACCES;
    - if (path.mnt->mnt_flags & MNT_NOEXEC)
    + if (pp->mnt->mnt_flags & MNT_NOEXEC)
    goto out_path_release;
    }

    @@ -343,11 +353,14 @@ SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
    * inherently racy and know that the fs may change
    * state before we even see this result.
    */
    - if (__mnt_is_readonly(path.mnt))
    + if (__mnt_is_readonly(pp->mnt))
    res = -EROFS;

    out_path_release:
    - path_put(&path);
    + if (file)
    + fput(file);
    + else
    + path_put(&path);
    out:
    revert_creds(old_cred);
    put_cred(override_cred);
    --
    1.7.1.331.ga5080


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