GHSA-WMCQ-6RPV-M375
Vulnerability from github – Published: 2026-09-25 12:31 – Updated: 2026-10-21 15:41In the Linux kernel, the following vulnerability has been resolved:
bpf: zero extend the result of an arena 32-bit cmpxchg
bpf_convert_ctx_accesses() rewrites an atomic on an arena pointer from BPF_STX | BPF_ATOMIC to BPF_STX | BPF_PROBE_ATOMIC, and it runs before bpf_opt_subreg_zext_lo32_rnd_hi32().
That pass emits an explicit zero extension for a 32-bit cmpxchg even when bpf_jit_needs_zext() is false. This is done because on some architectures 32-bit cmpxchg requires explicit zero extension for the dst register. E.g. on x86-64 'lock cmpxchg' does not change the %eax if comparison is successful, while BPF semantics declare that each operation on a 32-bit register zero extends it's upper half.
is_cmpxchg_insn() matches BPF_MODE == BPF_ATOMIC only, so an arena cmpxchg misses said zero extension adjustment. This patch adjusts is_cmpxchg_insn() to match BPF_PROBE_ATOMIC alongside BPF_ATOMIC.
{
"affected": [],
"aliases": [
"CVE-2026-98049"
],
"database_specific": {
"cwe_ids": [
"CWE-681"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-25T11:17:33Z",
"severity": "MODERATE"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: zero extend the result of an arena 32-bit cmpxchg\n\nbpf_convert_ctx_accesses() rewrites an atomic on an arena pointer from\nBPF_STX | BPF_ATOMIC to BPF_STX | BPF_PROBE_ATOMIC, and it runs before\nbpf_opt_subreg_zext_lo32_rnd_hi32().\n\nThat pass emits an explicit zero extension for a 32-bit cmpxchg even\nwhen bpf_jit_needs_zext() is false. This is done because on some\narchitectures 32-bit cmpxchg requires explicit zero extension for the\ndst register. E.g. on x86-64 \u0027lock cmpxchg\u0027 does not change the %eax\nif comparison is successful, while BPF semantics declare that each\noperation on a 32-bit register zero extends it\u0027s upper half.\n\nis_cmpxchg_insn() matches BPF_MODE == BPF_ATOMIC only, so an arena\ncmpxchg misses said zero extension adjustment. This patch adjusts\nis_cmpxchg_insn() to match BPF_PROBE_ATOMIC alongside BPF_ATOMIC.",
"id": "GHSA-wmcq-6rpv-m375",
"modified": "2026-10-21T15:41:39Z",
"published": "2026-09-25T12:31:34Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98049"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1bb1be18263995b159cf5afad3a05500ba6d2a7b"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/1c1b476d43a8b6c9bc04600369dd8cc39950d98e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4814ed6406f3493bd554ad046da5f7fc04833571"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/6bb6ae5ab1beffda51dabf41612f501d07f10fc6"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
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