CVE-2025-38255 Information

Jul 10, 2025 cve

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]

Reference

https://git.kernel.org/stable/c/29d39e0d5f16c060e32542b2cf351c09fd22b250 https://git.kernel.org/stable/c/64a99eff8dcf1f951a544e6058341b2b19a8fdbd https://git.kernel.org/stable/c/911ef2e8a7de5b2bae8ff11fb0bd01f699e6db65 https://git.kernel.org/stable/c/df831e97739405ecbaddb85516bc7d4d1c933d6b

CNNVD-202507-1297 (Published: 2025-07-09)

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