GHSA-CGJW-H652-C9Q2
Vulnerability from github – Published: 2025-08-19 18:31 – Updated: 2026-09-14 12:31In the Linux kernel, the following vulnerability has been resolved:
bpf: Reject narrower access to pointer ctx fields
The following BPF program, simplified from a syzkaller repro, causes a kernel warning:
r0 = *(u8 *)(r1 + 169);
exit;
With pointer field sk being at offset 168 in __sk_buff. This access is detected as a narrower read in bpf_skb_is_valid_access because it doesn't match offsetof(struct __sk_buff, sk). It is therefore allowed and later proceeds to bpf_convert_ctx_access. Note that for the "is_narrower_load" case in the convert_ctx_accesses(), the insn->off is aligned, so the cnt may not be 0 because it matches the offsetof(struct __sk_buff, sk) in the bpf_convert_ctx_access. However, the target_size stays 0 and the verifier errors with a kernel warning:
verifier bug: error during ctx access conversion(1)
This patch fixes that to return a proper "invalid bpf_context access off=X size=Y" error on the load instruction.
The same issue affects multiple other fields in context structures that allow narrow access. Some other non-affected fields (for sk_msg, sk_lookup, and sockopt) were also changed to use bpf_ctx_range_ptr for consistency.
Note this syzkaller crash was reported in the "Closes" link below, which used to be about a different bug, fixed in commit fce7bd8e385a ("bpf/verifier: Handle BPF_LOAD_ACQ instructions in insn_def_regno()"). Because syzbot somehow confused the two bugs, the new crash and repro didn't get reported to the mailing list.
{
"affected": [],
"aliases": [
"CVE-2025-38591"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-08-19T17:15:36Z",
"severity": "MODERATE"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Reject narrower access to pointer ctx fields\n\nThe following BPF program, simplified from a syzkaller repro, causes a\nkernel warning:\n\n r0 = *(u8 *)(r1 + 169);\n exit;\n\nWith pointer field sk being at offset 168 in __sk_buff. This access is\ndetected as a narrower read in bpf_skb_is_valid_access because it\ndoesn\u0027t match offsetof(struct __sk_buff, sk). It is therefore allowed\nand later proceeds to bpf_convert_ctx_access. Note that for the\n\"is_narrower_load\" case in the convert_ctx_accesses(), the insn-\u003eoff\nis aligned, so the cnt may not be 0 because it matches the\noffsetof(struct __sk_buff, sk) in the bpf_convert_ctx_access. However,\nthe target_size stays 0 and the verifier errors with a kernel warning:\n\n verifier bug: error during ctx access conversion(1)\n\nThis patch fixes that to return a proper \"invalid bpf_context access\noff=X size=Y\" error on the load instruction.\n\nThe same issue affects multiple other fields in context structures that\nallow narrow access. Some other non-affected fields (for sk_msg,\nsk_lookup, and sockopt) were also changed to use bpf_ctx_range_ptr for\nconsistency.\n\nNote this syzkaller crash was reported in the \"Closes\" link below, which\nused to be about a different bug, fixed in\ncommit fce7bd8e385a (\"bpf/verifier: Handle BPF_LOAD_ACQ instructions\nin insn_def_regno()\"). Because syzbot somehow confused the two bugs,\nthe new crash and repro didn\u0027t get reported to the mailing list.",
"id": "GHSA-cgjw-h652-c9q2",
"modified": "2026-09-14T12:31:27Z",
"published": "2025-08-19T18:31:33Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-38591"
},
{
"type": "WEB",
"url": "https://cert-portal.siemens.com/productcert/html/ssa-019113.html"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/058a0da4f6d916a79b693384111bb80a90d73763"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/202900ceeef67458c964c2af6e1427c8e533ea7c"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/33660d44e789edb4f303210c813fc56d56377a90"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7847c4140e06f6e87229faae22cc38525334c156"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e09299225d5ba3916c91ef70565f7d2187e4cca0"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e2e9599f3503df7cf3569d2b6c50d5488fb59435"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/feae34c992eb7191862fb1594c704fbbf650fef8"
}
],
"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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