On Tue, Jun 18, 2019 at 11:27 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > On Tue, Jun 18, 2019 at 8:07 PM syzbot > <syzbot+c277e8e2f46414645508@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > Hello, > > > > syzbot found the following crash on: > > > > HEAD commit: 963172d9 Merge branch 'x86-urgent-for-linus' of git://git... > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=17c090eaa00000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=fa9f7e1b6a8bb586 > > dashboard link: https://syzkaller.appspot.com/bug?extid=c277e8e2f46414645508 > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15a32f46a00000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13a7dc9ea00000 > > > > The bug was bisected to: > > > > commit 77115225acc67d9ac4b15f04dd138006b9cd1ef2 > > Author: Amir Goldstein <amir73il@xxxxxxxxx> > > Date: Thu Jan 10 17:04:37 2019 +0000 > > > > fanotify: cache fsid in fsnotify_mark_connector > > > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=12bfcb66a00000 > > final crash: https://syzkaller.appspot.com/x/report.txt?x=11bfcb66a00000 > > console output: https://syzkaller.appspot.com/x/log.txt?x=16bfcb66a00000 > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > Reported-by: syzbot+c277e8e2f46414645508@xxxxxxxxxxxxxxxxxxxxxxxxx > > Fixes: 77115225acc6 ("fanotify: cache fsid in fsnotify_mark_connector") > > > > WARNING: CPU: 0 PID: 8994 at fs/notify/fanotify/fanotify.c:359 > > fanotify_get_fsid fs/notify/fanotify/fanotify.c:359 [inline] > > Oops, we forgot to update conn->fsid when the first mark added > for inode has no fsid (e.g. inotify) and the second mark has fid, > which is more or less the only thing the repro does. > And if we are going to update conn->fsid, we do no have the > cmpxchg to guaranty setting fsid atomically. > > I am thinking a set-once flag on connector FSNOTIFY_CONN_HAS_FSID > checked before smp_rmb() in fanotify_get_fsid(). > If the flag is not set then call vfs_get_fsid() instead of using fsid cache. Actually, we don't need to call vfs_get_fsid() in race we just drop the event. > conn->fsid can be updated in fsnotify_add_mark_list() under conn->lock, > and flag set after smp_wmb(). > > Does that sound correct? > Something like this: #syz test: https://github.com/amir73il/linux.git fsnotify-fix-fsid-cache It passed my modified ltp test: https://github.com/amir73il/ltp/commits/fanotify_dirent Thanks, Amir.
