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

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Date: Thu, 11 Apr 2024 15:25:21 -0400
From: Gabriel Krisman Bertazi <krisman@...e.de>
To: Amir Goldstein <amir73il@...il.com>
Cc: Jan Kara <jack@...e.cz>,  syzbot
 <syzbot+5e3f9b2a67b45f16d4e6@...kaller.appspotmail.com>,
  linux-ext4@...r.kernel.org,  linux-fsdevel@...r.kernel.org,
  linux-kernel@...r.kernel.org,  repnop@...gle.com,
  syzkaller-bugs@...glegroups.com, khazhy@...omium.org
Subject: Re: [syzbot] [ext4?] KASAN: slab-use-after-free Read in fsnotify

Amir Goldstein <amir73il@...il.com> writes:

> On Thu, Apr 11, 2024 at 3:13 PM Jan Kara <jack@...e.cz> 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@...kaller.appspotmail.com
>> >
>> > 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?

I think it should be fine to exclude volumes being teared down.  Cc'ing
Khazhy, who sponsored this work at the time and owned the use-case.

-- 
Gabriel Krisman Bertazi