Re: WARNING in kmem_cache_free

[Dmitry Vyukov]

On Sun, Apr 8, 2018 at 8:01 AM, Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> On Fri, Apr 06, 2018 at 03:33:36PM +0200, Dmitry Vyukov wrote:
>> On Fri, Apr 6, 2018 at 3:24 PM, syzbot
>> <syzbot+75397ee3df5c70164154@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>> > Unfortunately, I don't have any reproducer for this crash yet.
>>
>> Interesting type of bug, I think we see this for the first time.
>
> Can you focus syzbot to try to find a reproducer?  This seems to be
> produced by calling mount() with a pathname that's somewhere between,
> say, 3950 & 4100 bytes long from a compat 32-bit task.


Something in the log definitely triggers a very bad heap corruption.

This can be reproduced following instructions at:
https://github.com/google/syzkaller/blob/master/docs/syzbot.md#syzkaller-reproducers

and then running:
./syz-execprog -sandbox=namespace -arch=386 -repeat=0 -procs=10 log.txt

where log.txt comes from "Raw console output" link.

Note that you need to build syzkaller with 'make TARGETARCH=386' and
the use bin/linux_386/syz-executor.

While running it I got:
BUG: KASAN: double-free or invalid-free in free_request_size+0x5b/0x70
block/blk-core.c:769
https://gist.githubusercontent.com/dvyukov/05f4e77a34795d329aa7a2f40265e396/raw/63a29123b79f1fbad3521d0ff034946be68bfd4a/gistfile1.txt

Then kernel BUG at mm/slab.c:4407!
https://gist.githubusercontent.com/dvyukov/5b3bcc90d326e9da3636aea2c95ace8f/raw/1589504c708994936681d61ba9d70029998b9b1a/gistfile1.txt

And then BUG: unable to handle kernel paging request at ffffebe000000020
https://gist.githubusercontent.com/dvyukov/72025b1c68e488f4fda243e0c152f044/raw/d2c171bc55ad3a43cea33095fa2eea48768b1131/gistfile1.txt

One interesting thing is that if I run the log once and it does not
crash, then when I try to start binary again I am getting:
[  456.837870] Invalid argument reading file caps for /root/syz-executor
The binary somehow becomes broken on disk...

I guess syzbot did find a reproducer in this log, but did not
attribute it to this bug as it causes crashes all over the place.