From: Ian Kent raven@themaw.net Subject: autofs: revert "autofs: fix AT_NO_AUTOMOUNT not being honored"

42f4614821 ("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.t... 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 ---

fs/namei.c | 15 +++------------ include/linux/fs.h | 3 ++- 2 files changed, 5 insertions(+), 13 deletions(-)

diff -puN fs/namei.c~autofs-revert-fix-at_no_automount-not-being-honored fs/namei.c --- a/fs/namei.c~autofs-revert-fix-at_no_automount-not-being-honored +++ a/fs/namei.c @@ -1129,18 +1129,9 @@ static int follow_automount(struct path * 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 -puN include/linux/fs.h~autofs-revert-fix-at_no_automount-not-being-honored include/linux/fs.h --- a/include/linux/fs.h~autofs-revert-fix-at_no_automount-not-being-honored +++ a/include/linux/fs.h @@ -3088,7 +3088,8 @@ static inline int vfs_lstat(const char _ 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) { _