From: Amir Goldstein <email@example.com> To: Jan Kara <firstname.lastname@example.org> Cc: linux-fsdevel <email@example.com> Subject: Re: Ignore mask handling in fanotify_group_event_mask() Date: Sat, 23 May 2020 20:14:58 +0300 Message-ID: <CAOQ4uxgBGTAnZUedY3dEwR9V=hdrr_4PH_snj9E=sz-_UuVzTg@mail.gmail.com> (raw) In-Reply-To: <CAOQ4uxirUfcpOdxFG9TAHUFSz+A5FMJdT=y4UKwpFUVov43nSA@mail.gmail.com> On Thu, May 21, 2020 at 9:10 PM Amir Goldstein <firstname.lastname@example.org> wrote: > > On Thu, May 21, 2020 at 7:24 PM Jan Kara <email@example.com> wrote: > > > > Hello Amir! > > > > I was looking into backporting of commit 55bf882c7f13dd "fanotify: fix > > merging marks masks with FAN_ONDIR" and realized one oddity in > > fanotify_group_event_mask(). The thing is: Even if the mark mask is such > > that current event shouldn't trigger on the mark, we still have to take > > mark's ignore mask into account. > > > > The most realistic example that would demonstrate the issue that comes to my > > mind is: > > > > mount mark watching for FAN_OPEN | FAN_ONDIR. > > inode mark on a directory with mask == 0 and ignore_mask == FAN_OPEN. > > > > I'd expect the group will not get any event for opening the dir but the > > code in fanotify_group_event_mask() would not prevent event generation. Now > > as I've tested the event currently actually does not get generated because > > there is a rough test in send_to_group() that actually finds out that there > > shouldn't be anything to report and so fanotify handler is actually never > > called in such case. But I don't think it's good to have an inconsistent > > test in fanotify_group_event_mask(). What do you think? > > > > I agree this is not perfect. > I think that moving the marks_ignored_mask line > To the top of the foreach loop should fix the broken logic. > It will not make the code any less complicated to follow though. > Perhaps with a comment along the lines of: > > /* Ignore mask is applied regardless of ISDIR and ON_CHILD flags */ > marks_ignored_mask |= mark->ignored_mask; > > Now is there a real bug here? > Probably not because send_to_group() always applied an ignore mask > that is greater or equal to that of fanotify_group_event_mask(). > That's a wrong statement of course. We do need to re-apply the ignore mask when narrowing the event mask. Exposing the bug requires a "compound" event. The only case of compound event I could think of is this: mount mark with mask == 0 and ignore_mask == FAN_OPEN. inode mark on a directory with mask == FAN_EXEC | FAN_EVENT_ON_CHILD. The event: FAN_OPEN | FAN_EXEC | FAN_EVENT_ON_CHILD would be reported to group with the FAN_OPEN flag despite the fact that FAN_OPEN is in ignore mask of mount mark because the mark iteration loop skips over non-inode marks for events on child. I'll try to work that case into the relevant LTP test to prove it and post a fix. Thanks, Amir.
next prev parent reply index Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-05-21 16:24 Jan Kara 2020-05-21 18:10 ` Amir Goldstein 2020-05-23 17:14 ` Amir Goldstein [this message] 2020-05-25 7:23 ` Jan Kara 2020-05-25 8:52 ` Amir Goldstein 2020-05-25 12:42 ` Jan Kara
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