Re: KASAN: null-ptr-deref Read in tcf_idrinfo_destroy

[Cong Wang]

On Wed, Feb 10, 2021 at 9:53 PM syzbot
<syzbot+151e3e714d34ae4ce7e8@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit:    291009f6 Merge tag 'pm-5.11-rc8' of git://git.kernel.org/p..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=14470d18d00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a53fd47f16f22f8c
> dashboard link: https://syzkaller.appspot.com/bug?extid=151e3e714d34ae4ce7e8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15f45814d00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15f4aff8d00000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+151e3e714d34ae4ce7e8@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ==================================================================
> BUG: KASAN: null-ptr-deref in instrument_atomic_read include/linux/instrumented.h:71 [inline]
> BUG: KASAN: null-ptr-deref in atomic_read include/asm-generic/atomic-instrumented.h:27 [inline]
> BUG: KASAN: null-ptr-deref in __tcf_idr_release net/sched/act_api.c:178 [inline]
> BUG: KASAN: null-ptr-deref in tcf_idrinfo_destroy+0x129/0x1d0 net/sched/act_api.c:598
> Read of size 4 at addr 0000000000000010 by task kworker/u4:5/204
>
> CPU: 0 PID: 204 Comm: kworker/u4:5 Not tainted 5.11.0-rc7-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: netns cleanup_net
> Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x107/0x163 lib/dump_stack.c:120
>  __kasan_report mm/kasan/report.c:400 [inline]
>  kasan_report.cold+0x5f/0xd5 mm/kasan/report.c:413
>  check_memory_region_inline mm/kasan/generic.c:179 [inline]
>  check_memory_region+0x13d/0x180 mm/kasan/generic.c:185
>  instrument_atomic_read include/linux/instrumented.h:71 [inline]
>  atomic_read include/asm-generic/atomic-instrumented.h:27 [inline]
>  __tcf_idr_release net/sched/act_api.c:178 [inline]
>  tcf_idrinfo_destroy+0x129/0x1d0 net/sched/act_api.c:598
>  tc_action_net_exit include/net/act_api.h:151 [inline]
>  police_exit_net+0x168/0x360 net/sched/act_police.c:390

This is really strange. It seems we still left some -EBUSY placeholders
in the idr, however, we actually call tcf_action_destroy() to clean up
everything including -EBUSY ones on error path.

What do you think, Vlad?

Thanks.