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

From: Vlad Buslov <[email-masked]>
Date: Tue, 16 Feb 2021 18:12:29 +0200

On Tue 16 Feb 2021 at 01:22, Cong Wang <[email-masked]> wrote:
> On Wed, Feb 10, 2021 at 9:53 PM syzbot
> <[email-masked]> 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: [email-masked]
>>
>> ==================================================================
>> 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.

Hi Cong,

I couldn't reproduce the issue with syzbot repro.c, but it looks like we
are missing tcf_idr_insert_many() in exts->police handling code inside
tcf_exts_validate() which calls tcf_action_init_1(). After recent
changes action is no longer inserted in idr by init_1 and requires
manual call to tcf_idr_insert_many(). I'll send a fix.

Regards,
Vlad