linux-kernel - Re: [PATCH net 0/2] Fix NPE discovered by running bpf kselftest

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Message-ID: <87y10e1fij.fsf@all.your.base.are.belong.to.us>
Date: Tue, 17 Dec 2024 16:43:48 +0100
From: Björn Töpel <bjorn@...nel.org>
To: Levi Zim <rsworktech@...look.com>, Cong Wang <xiyou.wangcong@...il.com>
Cc: John Fastabend <john.fastabend@...il.com>, Jakub Sitnicki
 <jakub@...udflare.com>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
 Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, David Ahern
 <dsahern@...nel.org>, netdev@...r.kernel.org, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 0/2] Fix NPE discovered by running bpf kselftest

Levi Zim <rsworktech@...look.com> writes:

> On 2024-12-04 09:01, Cong Wang wrote:
>> On Sun, Dec 01, 2024 at 09:42:08AM +0800, Levi Zim wrote:
>>> On 2024-11-30 21:38, Levi Zim via B4 Relay wrote:
>>>> I found that bpf kselftest sockhash::test_txmsg_cork_hangs in
>>>> test_sockmap.c triggers a kernel NULL pointer dereference:
>> Interesting, I also ran this test recently and I didn't see such a
>> crash.
>
> I am also curious about why other people or the CI didn't hit such crash.

FWIW, I'm hitting it on RISC-V:

  |  Unable to handle kernel access to user memory without uaccess routines at virtual address 0000000000000008
  |  Oops [#1]
  |  Modules linked in: sch_fq_codel drm fuse drm_panel_orientation_quirks backlight
  |  CPU: 7 UID: 0 PID: 732 Comm: test_sockmap Not tainted 6.13.0-rc3-00017-gf44d154d6e3d #1
  |  Hardware name: riscv-virtio qemu/qemu, BIOS 2025.01-rc3-00042-gacab6e78aca7 01/01/2025
  |  epc : splice_to_socket+0x376/0x49a
  |   ra : splice_to_socket+0x37c/0x49a
  |  epc : ffffffff803d9ffc ra : ffffffff803da002 sp : ff20000001c3b8b0
  |   gp : ffffffff827aefa8 tp : ff60000083450040 t0 : ff6000008a12d001
  |   t1 : 0000100100001001 t2 : 0000000000000000 s0 : ff20000001c3bae0
  |   s1 : ffffffffffffefff a0 : ff6000008245e200 a1 : ff60000087dd0450
  |   a2 : 0000000000000000 a3 : 0000000000000000 a4 : 0000000000000000
  |   a5 : 0000000000000000 a6 : ff20000001c3b450 a7 : ff6000008a12c004
  |   s2 : 000000000000000f s3 : ff6000008245e2d0 s4 : ff6000008245e280
  |   s5 : 0000000000000000 s6 : 0000000000000002 s7 : 0000000000001001
  |   s8 : 0000000000003001 s9 : 0000000000000002 s10: 0000000000000002
  |   s11: ff6000008245e200 t3 : ffffffff8001e78c t4 : 0000000000000000
  |   t5 : 0000000000000000 t6 : ff6000008869f230
  |  status: 0000000200000120 badaddr: 0000000000000008 cause: 000000000000000d
  |  [<ffffffff803d9ffc>] splice_to_socket+0x376/0x49a
  |  [<ffffffff803d8bc0>] direct_splice_actor+0x44/0x216
  |  [<ffffffff803d8532>] splice_direct_to_actor+0xb6/0x1e8
  |  [<ffffffff803d8780>] do_splice_direct+0x70/0xa2
  |  [<ffffffff80392e40>] do_sendfile+0x26e/0x2d4
  |  [<ffffffff803939d4>] __riscv_sys_sendfile64+0xf2/0x10e
  |  [<ffffffff80fdfb64>] do_trap_ecall_u+0x1f8/0x26c
  |  [<ffffffff80fedaee>] _new_vmalloc_restore_context_a0+0xc6/0xd2
  |  Code: c5d8 9e35 c590 8bb3 40db eb01 6998 b823 0005 856e (6718) 2d05 
  |  ---[ end trace 0000000000000000 ]---
  |  Kernel panic - not syncing: Fatal exception
  |  SMP: stopping secondary CPUs
  |  ---[ end Kernel panic - not syncing: Fatal exception ]---

This is commit f44d154d6e3d ("Merge tag 'soc-fixes-6.13' of
git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc").

(Yet to bisect!)


Björn