readlinkat(), fchownat() and fstatat() with empty relative pathnames

For readlinkat() we simply allow empty pathname; it will fail unless
we have dfd equal to O_PATH-opened symlink, so we are outside of
POSIX scope here.  For fchownat() and fstatat() we allow AT_EMPTY_PATH;
let the caller explicitly ask for such behaviour.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/open.c b/fs/open.c
index 14a51de..3cac0bd 100644 (file)
--- a/fs/open.c
+++ b/fs/open.c
@@ -573,13 +573,15 @@ SYSCALL_DEFINE5(fchownat, int, dfd, const char __user *, filename, uid_t, user,
 {
        struct path path;
        int error = -EINVAL;
-       int follow;
+       int lookup_flags;
 
-       if ((flag & ~AT_SYMLINK_NOFOLLOW) != 0)
+       if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
                goto out;
 
-       follow = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
-       error = user_path_at(dfd, filename, follow, &path);
+       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);

diff --git a/fs/stat.c b/fs/stat.c
index d5c61cf..9610391 100644 (file)
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -75,13 +75,16 @@ int vfs_fstatat(int dfd, const char __user *filename, struct kstat *stat,
        int error = -EINVAL;
        int lookup_flags = 0;
 
-       if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT)) != 0)
+       if ((flag & ~(AT_SYMLINK_NOFOLLOW | AT_NO_AUTOMOUNT |
+                     AT_EMPTY_PATH)) != 0)
                goto out;
 
        if (!(flag & AT_SYMLINK_NOFOLLOW))
                lookup_flags |= LOOKUP_FOLLOW;
        if (flag & AT_NO_AUTOMOUNT)
                lookup_flags |= LOOKUP_NO_AUTOMOUNT;
+       if (flag & AT_EMPTY_PATH)
+               lookup_flags |= LOOKUP_EMPTY;
 
        error = user_path_at(dfd, filename, lookup_flags, &path);
        if (error)
@@ -297,7 +300,7 @@ SYSCALL_DEFINE4(readlinkat, int, dfd, const char __user *, pathname,
        if (bufsiz <= 0)
                return -EINVAL;
 
-       error = user_path_at(dfd, pathname, 0, &path);
+       error = user_path_at(dfd, pathname, LOOKUP_EMPTY, &path);
        if (!error) {
                struct inode *inode = path.dentry->d_inode;