{"id":"CVE-2025-38255","title":"lib/group_cpus: fix NULL pointer dereference from group_cpus_evenly()","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nlib/group_cpus: fix NULL pointer dereference from group_cpus_evenly()\n\nWhile testing null_blk with configfs, echo 0 > poll_queues will trigger\nfollowing panic:\n\nBUG: ke…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 6a6dcae8f486c3f3298d0767d34505121c7b0b81 < 64a99eff8dcf1f951a544e6058341b2b19a8fdbd","Linux >= 6a6dcae8f486c3f3298d0767d34505121c7b0b81 < 29d39e0d5f16c060e32542b2cf351c09fd22b250","Linux >= 6a6dcae8f486c3f3298d0767d34505121c7b0b81 < 911ef2e8a7de5b2bae8ff11fb0bd01f699e6db65","Linux >= 6a6dcae8f486c3f3298d0767d34505121c7b0b81 < df831e97739405ecbaddb85516bc7d4d1c933d6b","Linux 6.3"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-11-05T20:52:25.572397Z"},"published":"2025-07-09","updated":"2026-11-05","sourceUpdated":"2026-11-05T21:02:29.328Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2025-38255","references":[{"url":"https://git.kernel.org/stable/c/64a99eff8dcf1f951a544e6058341b2b19a8fdbd"},{"url":"https://git.kernel.org/stable/c/29d39e0d5f16c060e32542b2cf351c09fd22b250"},{"url":"https://git.kernel.org/stable/c/911ef2e8a7de5b2bae8ff11fb0bd01f699e6db65"},{"url":"https://git.kernel.org/stable/c/df831e97739405ecbaddb85516bc7d4d1c933d6b"}],"tags":["cve.org"],"epss":0.00166,"epssPercentile":0.05828,"ingestedAt":"2026-11-05T22:38:31.945Z","slug":"CVE-2025-38255","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nlib/group_cpus: fix NULL pointer dereference from group_cpus_evenly()\n\nWhile testing null_blk with configfs, echo 0 > poll_queues will trigger\nfollowing panic:\n\nBUG: kernel NULL pointer dereference, address: 0000000000000010\nOops: Oops: 0000 [#1] SMP NOPTI\nCPU: 27 UID: 0 PID: 920 Comm: bash Not tainted 6.15.0-02023-gadbdb95c8696-dirty #1238 PREEMPT(undef)\nHardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014\nRIP: 0010:__bitmap_or+0x48/0x70\nCall Trace:\n <TASK>\n __group_cpus_evenly+0x822/0x8c0\n group_cpus_evenly+0x2d9/0x490\n blk_mq_map_queues+0x1e/0x110\n null_map_queues+0xc9/0x170 [null_blk]\n blk_mq_update_queue_map+0xdb/0x160\n blk_mq_update_nr_hw_queues+0x22b/0x560\n nullb_update_nr_hw_queues+0x71/0xf0 [null_blk]\n nullb_device_poll_queues_store+0xa4/0x130 [null_blk]\n configfs_write_iter+0x109/0x1d0\n vfs_write+0x26e/0x6f0\n ksys_write+0x79/0x180\n __x64_sys_write+0x1d/0x30\n x64_sys_call+0x45c4/0x45f0\n do_syscall_64+0xa5/0x240\n entry_SYSCALL_64_after_hwframe+0x76/0x7e\n\nRoot cause is that numgrps is set to 0, and ZERO_SIZE_PTR is returned from\nkcalloc(), and later ZERO_SIZE_PTR will be deferenced.\n\nFix the problem by checking numgrps first in group_cpus_evenly(), and\nreturn NULL directly if numgrps is zero.\n\n[yukuai3@huawei.com: also fix the non-SMP version]\n\n## Affected\n\n- `Linux >= 6a6dcae8f486c3f3298d0767d34505121c7b0b81 < 64a99eff8dcf1f951a544e6058341b2b19a8fdbd`\n- `Linux >= 6a6dcae8f486c3f3298d0767d34505121c7b0b81 < 29d39e0d5f16c060e32542b2cf351c09fd22b250`\n- `Linux >= 6a6dcae8f486c3f3298d0767d34505121c7b0b81 < 911ef2e8a7de5b2bae8ff11fb0bd01f699e6db65`\n- `Linux >= 6a6dcae8f486c3f3298d0767d34505121c7b0b81 < df831e97739405ecbaddb85516bc7d4d1c933d6b`\n- `Linux 6.3`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}