autofs: revert "autofs: fix AT_NO_AUTOMOUNT not being honored"

Commit 42f461482178 ("autofs: fix AT_NO_AUTOMOUNT not being honored")
allowed the fstatat(2) system call to properly honor the AT_NO_AUTOMOUNT
flag but introduced a semantic change.

In order to honor AT_NO_AUTOMOUNT a semantic change was made to the
negative dentry case for stat family system calls in follow_automount().

This changed the unconditional triggering of an automount in this case
to no longer be done and an error returned instead.

This has caused more problems than I expected so reverting the change is
needed.

In a discussion with Neil Brown it was concluded that the automount(8)
daemon can implement this change without kernel modifications.  So that
will be done instead and the autofs module documentation updated with a
description of the problem and what needs to be done by module users for
this specific case.

Link: http://lkml.kernel.org/r/151174730120.6162.3848002191530283984.stgit@pluto.themaw.net
Fixes: 42f4614821 ("autofs: fix AT_NO_AUTOMOUNT not being honored")
Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Neil Brown <neilb@suse.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: David Howells <dhowells@redhat.com>
Cc: Colin Walters <walters@redhat.com>
Cc: Ondrej Holy <oholy@redhat.com>
Cc: <stable@vger.kernel.org>	[4.11+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/namei.c b/fs/namei.c
index f0c7a7b9b6ca7562217746369cd8d5d82d43a99f..9cc91fb7f156541bd53243b35c2823bbf9ca1133 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1129,18 +1129,9 @@ static int follow_automount(struct path *path, struct nameidata *nd,
         * of the daemon to instantiate them before they can be used.
         */
        if (!(nd->flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |
-                          LOOKUP_OPEN | LOOKUP_CREATE |
-                          LOOKUP_AUTOMOUNT))) {
-               /* Positive dentry that isn't meant to trigger an
-                * automount, EISDIR will allow it to be used,
-                * otherwise there's no mount here "now" so return
-                * ENOENT.
-                */
-               if (path->dentry->d_inode)
-                       return -EISDIR;
-               else
-                       return -ENOENT;
-       }
+                          LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) &&
+           path->dentry->d_inode)
+               return -EISDIR;
 
        if (path->dentry->d_sb->s_user_ns != &init_user_ns)
                return -EACCES;

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9dc498d16cc147e9fbee218163598863cd785074..511fbaabf6248b67220c16653e491f74e3f046e7 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3088,7 +3088,8 @@ static inline int vfs_lstat(const char __user *name, struct kstat *stat)
 static inline int vfs_fstatat(int dfd, const char __user *filename,
                              struct kstat *stat, int flags)
 {
-       return vfs_statx(dfd, filename, flags, stat, STATX_BASIC_STATS);
+       return vfs_statx(dfd, filename, flags | AT_NO_AUTOMOUNT,
+                        stat, STATX_BASIC_STATS);
 }
 static inline int vfs_fstat(int fd, struct kstat *stat)
 {