Messages in this thread Patch in this message | | | Date | Wed, 27 Oct 2021 20:20:08 +0200 | Subject | Re: [syzbot] KASAN: slab-out-of-bounds Read in copy_data | From | Laurent Vivier <> |
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On 27/10/2021 19:03, Laurent Vivier wrote: > On 27/10/2021 18:25, Laurent Vivier wrote: >> On 27/10/2021 17:28, Michael S. Tsirkin wrote: >>> On Wed, Oct 27, 2021 at 03:36:19PM +0200, Dmitry Vyukov wrote: >>>> On Wed, 27 Oct 2021 at 15:11, Laurent Vivier <lvivier@redhat.com> wrote: >>>>> >>>>> On 26/10/2021 18:39, syzbot wrote: >>>>>> Hello, >>>>>> >>>>>> syzbot found the following issue on: >>>>>> >>>>>> HEAD commit: 9ae1fbdeabd3 Add linux-next specific files for 20211025 >>>>>> git tree: linux-next >>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=1331363cb00000 >>>>>> kernel config: https://syzkaller.appspot.com/x/.config?x=aeb17e42bc109064 >>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=b86736b5935e0d25b446 >>>>>> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for >>>>>> Debian) 2.35.2 >>>>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=116ce954b00000 >>>>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=132fcf62b00000 >>>>>> >>>>>> The issue was bisected to: >>>>>> >>>>>> commit 22849b5ea5952d853547cc5e0651f34a246b2a4f >>>>>> Author: Leon Romanovsky <leonro@nvidia.com> >>>>>> Date: Thu Oct 21 14:16:14 2021 +0000 >>>>>> >>>>>> devlink: Remove not-executed trap policer notifications >>>>>> >>>>>> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=137d8bfcb00000 >>>>>> final oops: https://syzkaller.appspot.com/x/report.txt?x=10fd8bfcb00000 >>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=177d8bfcb00000 >>>>>> >>>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit: >>>>>> Reported-by: syzbot+b86736b5935e0d25b446@syzkaller.appspotmail.com >>>>>> Fixes: 22849b5ea595 ("devlink: Remove not-executed trap policer notifications") >>>>>> >>>>>> ================================================================== >>>>>> BUG: KASAN: slab-out-of-bounds in memcpy include/linux/fortify-string.h:225 [inline] >>>>>> BUG: KASAN: slab-out-of-bounds in copy_data+0xf3/0x2e0 >>>>>> drivers/char/hw_random/virtio-rng.c:68 >>>>>> Read of size 64 at addr ffff88801a7a1580 by task syz-executor989/6542 >>>>>> >>>>> >>>>> I'm not able to reproduce the problem with next-20211026 and the C reproducer. >>>>> >>>>> And reviewing the code in copy_data() I don't see any issue. >>>>> >>>>> Is it possible to know what it the VM configuration used to test it? >>>> >>>> Hi Laurent, >>>> >>>> syzbot used e2-standard-2 GCE VM when that happened. >>>> You can see some info about these VMs under the "VM info" link on the dashboard. >>> >>> Could you pls confirm whether reverting >>> caaf2874ba27b92bca6f0298bf88bad94067ec37 addresses this? >>> >> >> I've restarted the syzbot on top of "hwrng: virtio - don't wait on cleanup" [1] and the >> problem has not been triggered. >> >> See https://syzkaller.appspot.com/bug?extid=b86736b5935e0d25b446 > > The problem seems to be introduced by the last patch: > > "hwrng: virtio - always add a pending request"
I think I understand the problem.
As we check data_avail != 0 before waiting on the completion, we can have a data_idx != 0.
The following change fixes the problem for me:
--- a/drivers/char/hw_random/virtio-rng.c +++ b/drivers/char/hw_random/virtio-rng.c @@ -52,6 +52,8 @@ static void request_entropy(struct virtrng_info *vi) struct scatterlist sg;
reinit_completion(&vi->have_data); + vi->data_avail = 0; + vi->data_idx = 0;
sg_init_one(&sg, vi->data, sizeof(vi->data));
MST, do you update the patch or do you want I send a new version?
Thanks, Laurent
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