From 42f46148217865a545e129612075f3d828a2c4e4 Mon Sep 17 00:00:00 2001 From: Ian Kent Date: Fri, 8 Sep 2017 16:16:24 -0700 Subject: [PATCH] autofs: fix AT_NO_AUTOMOUNT not being honored The fstatat(2) and statx() calls can pass the flag AT_NO_AUTOMOUNT which is meant to clear the LOOKUP_AUTOMOUNT flag and prevent triggering of an automount by the call. But this flag is unconditionally cleared for all stat family system calls except statx(). stat family system calls have always triggered mount requests for the negative dentry case in follow_automount() which is intended but prevents the fstatat(2) and statx() AT_NO_AUTOMOUNT case from being handled. In order to handle the AT_NO_AUTOMOUNT for both system calls the negative dentry case in follow_automount() needs to be changed to return ENOENT when the LOOKUP_AUTOMOUNT flag is clear (and the other required flags are clear). AFAICT this change doesn't have any noticable side effects and may, in some use cases (although I didn't see it in testing) prevent unnecessary callbacks to the automount daemon. It's also possible that a stat family call has been made with a path that is in the process of being mounted by some other process. But stat family calls should return the automount state of the path as it is "now" so it shouldn't wait for mount completion. This is the same semantic as the positive dentry case already handled. Link: http://lkml.kernel.org/r/150216641255.11652.4204561328197919771.stgit@pluto.themaw.net Fixes: deccf497d804a4c5fca ("Make stat/lstat/fstatat pass AT_NO_AUTOMOUNT to vfs_statx()") Signed-off-by: Ian Kent Cc: David Howells Cc: Colin Walters Cc: Ondrej Holy Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/namei.c | 15 ++++++++++++--- include/linux/fs.h | 3 +-- 2 files changed, 13 insertions(+), 5 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index ddb6a7c2b3d4..1180f9c58093 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1129,9 +1129,18 @@ 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)) && - path->dentry->d_inode) - return -EISDIR; + 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; + } 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 6111976848ff..2d0e6748e46e 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -3043,8 +3043,7 @@ 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 | AT_NO_AUTOMOUNT, - stat, STATX_BASIC_STATS); + return vfs_statx(dfd, filename, flags, stat, STATX_BASIC_STATS); } static inline int vfs_fstat(int fd, struct kstat *stat) {