Re: [syzbot] [ext4?] KASAN: slab-use-after-free Read in fsnotify

[Amir Goldstein]

On Thu, Apr 11, 2024 at 3:13 PM Jan Kara <jack@xxxxxxx> wrote:
>
> On Thu 11-04-24 01:11:20, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    6ebf211bb11d Add linux-next specific files for 20240410
> > git tree:       linux-next
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=12be955d180000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=16ca158ef7e08662
> > dashboard link: https://syzkaller.appspot.com/bug?extid=5e3f9b2a67b45f16d4e6
> > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13c91175180000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1621af9d180000
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/b050f81f73ed/disk-6ebf211b.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/412c9b9a536e/vmlinux-6ebf211b.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/016527216c47/bzImage-6ebf211b.xz
> > mounted in repro: https://storage.googleapis.com/syzbot-assets/75ad050c9945/mount_0.gz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+5e3f9b2a67b45f16d4e6@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > Quota error (device loop0): do_check_range: Getting block 0 out of range 1-5
> > EXT4-fs error (device loop0): ext4_release_dquot:6905: comm kworker/u8:4: Failed to release dquot type 1
> > ==================================================================
> > BUG: KASAN: slab-use-after-free in fsnotify+0x2a4/0x1f70 fs/notify/fsnotify.c:539
> > Read of size 8 at addr ffff88802f1dce80 by task kworker/u8:4/62
> >
> > CPU: 0 PID: 62 Comm: kworker/u8:4 Not tainted 6.9.0-rc3-next-20240410-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
> > Workqueue: events_unbound quota_release_workfn
> > Call Trace:
> >  <TASK>
> >  __dump_stack lib/dump_stack.c:88 [inline]
> >  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
> >  print_address_description mm/kasan/report.c:377 [inline]
> >  print_report+0x169/0x550 mm/kasan/report.c:488
> >  kasan_report+0x143/0x180 mm/kasan/report.c:601
> >  fsnotify+0x2a4/0x1f70 fs/notify/fsnotify.c:539
> >  fsnotify_sb_error include/linux/fsnotify.h:456 [inline]
> >  __ext4_error+0x255/0x3b0 fs/ext4/super.c:843
> >  ext4_release_dquot+0x326/0x450 fs/ext4/super.c:6903
> >  quota_release_workfn+0x39f/0x650 fs/quota/dquot.c:840
> >  process_one_work kernel/workqueue.c:3218 [inline]
> >  process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3299
> >  worker_thread+0x86d/0xd70 kernel/workqueue.c:3380
> >  kthread+0x2f0/0x390 kernel/kthread.c:389
> >  ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
> >  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> >  </TASK>
>
> Amir, I believe this happens on umount when the filesystem calls
> fsnotify_sb_error() after calling fsnotify_sb_delete(). In theory these two
> calls can even run in parallel and fsnotify() can be holding
> fsnotify_sb_info pointer while fsnotify_sb_delete() is freeing it so we
> need to figure out some proper synchronization for that...

Is it really needed to handle any for non SB_ACTIVE sb?
How about something like this?
Is that enough? or more synchronization is needed?

#syz test: https://github.com/amir73il/linux fsnotify-fixes

Thanks,
Amir.