linux-kernel - Re: [syzbot] [io-uring?] BUG: unable to handle kernel NULL pointer dereference in io_buffer

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <991ce8af-860b-41ec-9347-b5733d8259fe@gmail.com>
Date: Mon, 12 May 2025 15:19:41 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Jens Axboe <axboe@...nel.dk>,
 syzbot <syzbot+6456a99dfdc2e78c4feb@...kaller.appspotmail.com>,
 io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
 syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [io-uring?] BUG: unable to handle kernel NULL pointer
 dereference in io_buffer_select

On 5/12/25 14:56, Jens Axboe wrote:
> On 5/11/25 6:22 AM, Pavel Begunkov wrote:
>> On 5/11/25 01:19, syzbot wrote:
...>> this line:
>>
>> tail = smp_load_acquire(&br->tail);
>>
>> The offset of the tail field is 0xe so bl->buf_ring should be 0. That's
>> while it has IOBL_BUF_RING flag set. Same goes for the other report. Also,
>> since it's off io_buffer_select(), which looks up the list every time we
>> can exclude the req having a dangling pointer.
> 
> It's funky for sure, the other one is regular classic provided buffers.
> Interestingly, both reports are for arm32...

The other is ring pbuf as well

io_uring_register$IORING_REGISTER_PBUF_RING(r0, 0x16, &(0x7f0000000040)={&(0x7f0000001000)={[{0x0, 0x0, 0x3, 0x700}]}, 0x1, 0x1}, 0x1)

PC is at io_ring_buffers_peek+0x24/0x258 io_uring/kbuf.c:227

Also "tail = smp_load_acquire(&br->tail);"

-- 
Pavel Begunkov