CVE-2025-38255

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

MEDIUM

5.5

CVSS Score

Published: July 9, 2025 at 10:42 AM UTC

Updated: June 17, 2026 at 09:16 AM UTC

1 product affected across 1 vendorLinux Kernel

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Severity

MEDIUM5.5

Exploit prediction

EPSS 0.2%

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: <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(), 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. [[email protected]: also fix the non-SMP version]

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Linux Kernel · Linux

95%

6.13 ≤ v < 6.15.56.3 ≤ v < 6.12.366.3 ≤ v < 6.15.56.3 ≤ v < 6.166.3 ≤ v < 6.6.966.7 ≤ v < 6.12.366.16 rc1 6.16 rc2 6.16 rc3 6.36a6dcae8f486c3f3298d0767d34505121c7b0b81

Vendor states this is fixed in 29d39e0d5f16c060e32542b2cf351c09fd22b250 (fixed)

Vendor states this is fixed in 64a99eff8dcf1f951a544e6058341b2b19a8fdbd (fixed)

Vendor states this is fixed in 911ef2e8a7de5b2bae8ff11fb0bd01f699e6db65 (fixed)

Vendor states this is fixed in df831e97739405ecbaddb85516bc7d4d1c933d6b (fixed)

Vendor states this is fixed in 6.12.36 (unaffected)

Vendor states this is fixed in 6.15.5 (unaffected)

Vendor states this is fixed in 6.16 (unaffected)

Vendor states this is fixed in 6.3 (unaffected)

Vendor states this is fixed in 6.6.96 (unaffected)