Re: [PATCH 3/6] audit: Fix possible tagging failures

Jan Kara
2018-07-04T08:28:40Z

On Tue 03-07-18 20:42:26, Amir Goldstein wrote:
> On Tue, Jul 3, 2018 at 5:21 PM, Jan Kara <jack@suse.cz> wrote:
> > On Fri 29-06-18 15:05:07, Amir Goldstein wrote:
> >> On Thu, Jun 28, 2018 at 7:40 PM, Jan Kara <jack@suse.cz> wrote:
> >> > Audit tree code is replacing marks attached to inodes in non-atomic way.
> >> > Thus fsnotify_find_mark() in tag_chunk() may find a mark that belongs to
> >> > a chunk that is no longer valid one and will soon be destroyed. Tags
> >> > added to such chunk will be simply lost.
> >> >
> >> > Fix the problem by making sure old mark is marked as going away (through
> >> > fsnotify_detach_mark()) before dropping mark_mutex and thus in an atomic
> >> > way wrt tag_chunk(). Note that this does not fix the problem completely
> >> > as if tag_chunk() finds a mark that is going away, it fails with
> >> > -ENOENT. But at least the failure is not silent and currently there's no
> >> > way to search for another fsnotify mark attached to the inode. We'll fix
> >> > this problem in later patch.
> >> >
> >> > Signed-off-by: Jan Kara <jack@suse.cz>
> >> > ---
> >>
> >> This one too looks sane.
> >> Without knowing anything about audit_watch, there seems to be
> >> an fsnotify_destroy_mark() after unlock of audit_filter_mutex, so it
> >> may require a similar fix.
> >
> > Where? I don't see any call to fsnotify_destroy_mark() left after this
> > patch...
> >
>
> Not directly related to this cleanup, but looking in other audit modules,
> fsnotify_destroy_mark() in audit_remove_parent_watches() is called
> outside audit_filter_mutex and audit_find_parent() in audit_add_watch()
> is called inside audit_filter_mutex, so I was wondering if there was a
> similar race window in that code. I didn't spend enough time looking
> at audit_watch.c to understand what is going on in there.

Oh, those are completely different fsnotify marks :) They belong to
audit_watch_group (while these to audit_tree_group) and these patches have
no ambition to change anything there.

Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR