When a file is opened and created with open(..., O_CREAT) we get
both the CREATE and OPEN fsnotify events and would expect them in that
order. For most filesystems we get them in that order because
open_last_lookups() calls fsnofify_create() and then do_open() (from
path_openat()) calls vfs_open()->do_dentry_open() which calls
fsnotify_open().
However when ->atomic_open is used, the
do_dentry_open() -> fsnotify_open()
call happens from finish_open() which is called from the ->atomic_open
handler in lookup_open() which is called *before* open_last_lookups()
calls fsnotify_create(). So we get the "open" notification before
"create" - which is backwards. ltp testcase inotify02 tests this and
reports the inconsistency.
This patch lifts the fsnotify_open() call out of do_dentry_open() and
places it higher up the call stack. There are three callers of
do_dentry_open().
For vfs_open() and kernel_file_open() the fsnotify_open() is placed
directly in that caller so there should be no behavioural change.
For finish_open() there are three cases:
- finish_open is used in ->atomic_open handlers. For these we add a
call to fsnotify_open() in do_open() if FMODE_OPENED is set - which
means do_dentry_open() has been called. This happens after fsnotify_create().
- finish_open is used in ->tmpfile() handlers. For these a call to
fsnotify_open() is added to vfs_tmpfile()
- finish_open is used in gfs2_create_inode() which is used for
atomic_open, but also for gfs2_create() which is a ->create handler
and is not expected to open the file. So losing the fsnotify_open()
call in this case seems correct.
With this patch NFSv3 is restored to its previous behaviour (before
->atomic_open support was added) of generating CREATE notifications
before OPEN, and NFSv4 now has that same correct ordering that is has
not had before. I haven't tested other filesystems.
Fixes: 7c6c5249f061 ("NFS: add atomic_open for NFSv3 to handle O_TRUNC correctly.")
Reported-by: James Clark <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]
Signed-off-by: NeilBrown <[email protected]>
---
fs/namei.c | 9 +++++++--
fs/open.c | 19 ++++++++++++-------
2 files changed, 19 insertions(+), 9 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index 37fb0a8aa09a..32031feaf6b6 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3646,8 +3646,12 @@ static int do_open(struct nameidata *nd,
do_truncate = true;
}
error = may_open(idmap, &nd->path, acc_mode, open_flag);
- if (!error && !(file->f_mode & FMODE_OPENED))
- error = vfs_open(&nd->path, file);
+ if (!error) {
+ if (file->f_mode & FMODE_OPENED)
+ fsnotify_open(file);
+ else
+ error = vfs_open(&nd->path, file);
+ }
if (!error)
error = security_file_post_open(file, op->acc_mode);
if (!error && do_truncate)
@@ -3706,6 +3710,7 @@ int vfs_tmpfile(struct mnt_idmap *idmap,
error = may_open(idmap, &file->f_path, 0, file->f_flags);
if (error)
return error;
+ fsnotify_open(file);
inode = file_inode(file);
if (!(open_flag & O_EXCL)) {
spin_lock(&inode->i_lock);
diff --git a/fs/open.c b/fs/open.c
index 89cafb572061..970f299c0e77 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1004,11 +1004,6 @@ static int do_dentry_open(struct file *f,
}
}
- /*
- * Once we return a file with FMODE_OPENED, __fput() will call
- * fsnotify_close(), so we need fsnotify_open() here for symmetry.
- */
- fsnotify_open(f);
return 0;
cleanup_all:
@@ -1085,8 +1080,17 @@ EXPORT_SYMBOL(file_path);
*/
int vfs_open(const struct path *path, struct file *file)
{
+ int ret;
+
file->f_path = *path;
- return do_dentry_open(file, NULL);
+ ret = do_dentry_open(file, NULL);
+ if (!ret)
+ /*
+ * Once we return a file with FMODE_OPENED, __fput() will call
+ * fsnotify_close(), so we need fsnotify_open() here for symmetry.
+ */
+ fsnotify_open(file);
+ return ret;
}
struct file *dentry_open(const struct path *path, int flags,
@@ -1178,7 +1182,8 @@ struct file *kernel_file_open(const struct path *path, int flags,
if (error) {
fput(f);
f = ERR_PTR(error);
- }
+ } else
+ fsnotify_open(f);
return f;
}
EXPORT_SYMBOL_GPL(kernel_file_open);
--
2.44.0
On Wed, 12 Jun 2024, Al Viro wrote:
> On Wed, Jun 12, 2024 at 12:05:11PM +1000, NeilBrown wrote:
>
> > For finish_open() there are three cases:
> > - finish_open is used in ->atomic_open handlers. For these we add a
> > call to fsnotify_open() in do_open() if FMODE_OPENED is set - which
> > means do_dentry_open() has been called. This happens after fsnotify_create().
>
> Hummm.... There's a bit of behaviour change; in case we fail in
> may_open(), we used to get fsnotify_open()+fsnotify_close() and with that
> patch we's get fsnotify_close() alone.
True. Presumably we could fix that by doing
diff --git a/fs/namei.c b/fs/namei.c
index 37fb0a8aa09a..6fd04c9046fa 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3645,6 +3645,8 @@ static int do_open(struct nameidata *nd,
return error;
do_truncate = true;
}
+ if (file->f_mode & FMODE_OPENED)
+ fsnotify_open(file);
error = may_open(idmap, &nd->path, acc_mode, open_flag);
if (!error && !(file->f_mode & FMODE_OPENED))
error = vfs_open(&nd->path, file);
@@ -3702,6 +3704,7 @@ int vfs_tmpfile(struct mnt_idmap *idmap,
dput(child);
if (error)
return error;
+ fsnotify_open(file);
/* Don't check for other permissions, the inode was just created */
error = may_open(idmap, &file->f_path, 0, file->f_flags);
if (error)
instead, but it seems a little weird sending an OPEN notification if
may_open() fails.
>
> IF we don't care about that, we might as well take fsnotify_open()
> out of vfs_open() and, for do_open()/do_tmpfile()/do_o_path(), into
> path_openat() itself. I mean, having
> if (likely(!error)) {
> if (likely(file->f_mode & FMODE_OPENED)) {
> fsnotify_open(file);
> return file;
> }
> in there would be a lot easier to follow... It would lose fsnotify_open()
> in a few more failure exits, but if we don't give a damn about having it
> paired with fsnotify_close()...
>
Should we have fsnotify_open() set a new ->f_mode flag, and
fsnotify_close() abort if it isn't set (and clear it if it is)?
Then we would be guaranteed a balance - which does seem like a good
idea.
Thanks,
NeilBrown
On Wed, Jun 12, 2024 at 12:55:40PM +1000, NeilBrown wrote:
> > IF we don't care about that, we might as well take fsnotify_open()
> > out of vfs_open() and, for do_open()/do_tmpfile()/do_o_path(), into
> > path_openat() itself. I mean, having
> > if (likely(!error)) {
> > if (likely(file->f_mode & FMODE_OPENED)) {
> > fsnotify_open(file);
> > return file;
> > }
> > in there would be a lot easier to follow... It would lose fsnotify_open()
> > in a few more failure exits, but if we don't give a damn about having it
> > paired with fsnotify_close()...
> >
>
> Should we have fsnotify_open() set a new ->f_mode flag, and
> fsnotify_close() abort if it isn't set (and clear it if it is)?
> Then we would be guaranteed a balance - which does seem like a good
> idea.
Umm... In that case, I would rather have FMODE_NONOTIFY set just before
the fput() in path_openat() - no need to grab another flag from ->f_mode
(not a lot of unused ones there) and no need to add any overhead on
the fast path.
On Wed, Jun 12, 2024 at 12:05:11PM +1000, NeilBrown wrote:
> For finish_open() there are three cases:
> - finish_open is used in ->atomic_open handlers. For these we add a
> call to fsnotify_open() in do_open() if FMODE_OPENED is set - which
> means do_dentry_open() has been called. This happens after fsnotify_create().
Hummm.... There's a bit of behaviour change; in case we fail in
may_open(), we used to get fsnotify_open()+fsnotify_close() and with that
patch we's get fsnotify_close() alone.
IF we don't care about that, we might as well take fsnotify_open()
out of vfs_open() and, for do_open()/do_tmpfile()/do_o_path(), into
path_openat() itself. I mean, having
if (likely(!error)) {
if (likely(file->f_mode & FMODE_OPENED)) {
fsnotify_open(file);
return file;
}
in there would be a lot easier to follow... It would lose fsnotify_open()
in a few more failure exits, but if we don't give a damn about having it
paired with fsnotify_close()...
On Wed, 12 Jun 2024, Al Viro wrote:
> On Wed, Jun 12, 2024 at 12:55:40PM +1000, NeilBrown wrote:
> > > IF we don't care about that, we might as well take fsnotify_open()
> > > out of vfs_open() and, for do_open()/do_tmpfile()/do_o_path(), into
> > > path_openat() itself. I mean, having
> > > if (likely(!error)) {
> > > if (likely(file->f_mode & FMODE_OPENED)) {
> > > fsnotify_open(file);
> > > return file;
> > > }
> > > in there would be a lot easier to follow... It would lose fsnotify_open()
> > > in a few more failure exits, but if we don't give a damn about having it
> > > paired with fsnotify_close()...
> > >
> >
> > Should we have fsnotify_open() set a new ->f_mode flag, and
> > fsnotify_close() abort if it isn't set (and clear it if it is)?
> > Then we would be guaranteed a balance - which does seem like a good
> > idea.
>
> Umm... In that case, I would rather have FMODE_NONOTIFY set just before
> the fput() in path_openat() - no need to grab another flag from ->f_mode
> (not a lot of unused ones there) and no need to add any overhead on
> the fast path.
>
Unfortunately that gets messy if handle_truncate() fails. We would need
to delay the fsnotify_open() until after truncate which means moving it
out of vfs_open() or maybe calling do_dentry_open() directly from
do_open() - neither of which I like.
I think it is best to stick with "if FMODE_OPENED is set, then we call
fsnotify_open() even if the open will fail", and only move the place
where fsnotify_open() is called.
BTW I was wrong about gfs. Closer inspection of the code show that
finish_open() is only called in the ->atomic_open case.
Thanks,
NeilBrown