CVE-2025-38255 – Linux Kernel null_blk Configfs Null Pointer Dereference Vulnerability

CVE ID : CVE-2025-38255

Published : July 9, 2025, 11:15 a.m. | 49 minutes ago

Description : In the Linux kernel, the following vulnerability has been resolved:

lib/group_cpus: fix NULL pointer dereference from group_cpus_evenly()

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:

__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(), and later ZERO_SIZE_PTR will be deferenced.

Fix the problem by checking numgrps first in group_cpus_evenly(), and
return NULL directly if numgrps is zero.

[yukuai3@huawei.com: also fix the non-SMP version]
Severity: 0.0 | NA

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