linux-kernel - Re: [PATCH v2] lib/group_cpus: fix NULL pointer dereference from group_cpus

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: <CAFj5m9JBoY1ZPQ5oYh2RwMN9o_HEOofCge1LLPF1_Oh8AdP=Aw@mail.gmail.com>
Date: Thu, 19 Jun 2025 21:45:04 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: tglx@...utronix.de, akpm@...ux-foundation.org, john.g.garry@...cle.com, 
	axboe@...nel.dk, linux-kernel@...r.kernel.org, yukuai3@...wei.com, 
	yi.zhang@...wei.com, yangerkun@...wei.com, johnny.chenyi@...wei.com
Subject: Re: [PATCH v2] lib/group_cpus: fix NULL pointer dereference from group_cpus_evenly()

On Thu, Jun 19, 2025 at 9:33 PM Yu Kuai <yukuai1@...weicloud.com> wrote:
>
> From: Yu Kuai <yukuai3@...wei.com>
>
> While testing null_blk with configfs, echo 0 > poll_queues will trigger
> following panic:
>
> BUG: kernel NULL pointer dereference, address: 0000000000000010
> Oops: Oops: 0000 [#1] SMP NOPTI
> CPU: 27 UID: 0 PID: 920 Comm: bash Not tainted 6.15.0-02023-gadbdb95c8696-dirty #1238 PREEMPT(undef)
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014
> RIP: 0010:__bitmap_or+0x48/0x70
> Call Trace:
>  <TASK>
>  __group_cpus_evenly+0x822/0x8c0
>  group_cpus_evenly+0x2d9/0x490
>  blk_mq_map_queues+0x1e/0x110
>  null_map_queues+0xc9/0x170 [null_blk]
>  blk_mq_update_queue_map+0xdb/0x160
>  blk_mq_update_nr_hw_queues+0x22b/0x560
>  nullb_update_nr_hw_queues+0x71/0xf0 [null_blk]
>  nullb_device_poll_queues_store+0xa4/0x130 [null_blk]
>  configfs_write_iter+0x109/0x1d0
>  vfs_write+0x26e/0x6f0
>  ksys_write+0x79/0x180
>  __x64_sys_write+0x1d/0x30
>  x64_sys_call+0x45c4/0x45f0
>  do_syscall_64+0xa5/0x240
>  entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> Root cause is that numgrps is set to 0, and ZERO_SIZE_PTR is returned
> from kcalloc(), then __group_cpus_evenly() will deference the
> ZERO_SIZE_PTR.
>
> Fix the problem by checking numgrps first in group_cpus_evenly(), and
> return NULL directly if numgrps is zero.
>
> Fixes: 6a6dcae8f486 ("blk-mq: Build default queue map via group_cpus_evenly()")
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
> Changes in v2:
>  - check numgrps directly.
>
>  lib/group_cpus.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/lib/group_cpus.c b/lib/group_cpus.c
> index ee272c4cefcc..d68407e3601e 100644
> --- a/lib/group_cpus.c
> +++ b/lib/group_cpus.c
> @@ -352,6 +352,9 @@ struct cpumask *group_cpus_evenly(unsigned int numgrps)
>         int ret = -ENOMEM;
>         struct cpumask *masks = NULL;
>
> +       if (numgrps == 0)
> +               return NULL;
> +

Reviewed-by: Ming Lei <ming.lei@...hat.com>

Thanks,