GHSA-3Q38-VXGF-8598
Vulnerability from github – Published: 2026-09-25 12:31 – Updated: 2026-09-25 12:31In the Linux kernel, the following vulnerability has been resolved:
bpf: Reject tail calls directly from callback frames
A tail call from a non-zero frame is modeled as a return from that frame. The verifier makes R0 unknown and calls prepare_func_exit() for the taken branch.
When the current frame is a synchronous callback, prepare_func_exit() enforces the callback return-value contract and marks R0 precise. Since the tail-call path synthesized R0 rather than deriving it from an instruction, precision backtracking reaches the callback-calling instruction with R0 still requested and triggers the "callback unexpected regs" verifier bug. A CAP_BPF task can therefore cause a WARN and an -EFAULT BPF_PROG_LOAD.
Tail calls reachable from callbacks are already rejected later by check_max_stack_depth(). Reject a tail call made directly by a callback before constructing the inconsistent return state, using the existing diagnostic. Tail calls from ordinary subprograms keep their current behavior.
{
"affected": [],
"aliases": [
"CVE-2026-98061"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-25T11:17:35Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Reject tail calls directly from callback frames\n\nA tail call from a non-zero frame is modeled as a return from that frame.\nThe verifier makes R0 unknown and calls prepare_func_exit() for the taken\nbranch.\n\nWhen the current frame is a synchronous callback, prepare_func_exit()\nenforces the callback return-value contract and marks R0 precise. Since the\ntail-call path synthesized R0 rather than deriving it from an instruction,\nprecision backtracking reaches the callback-calling instruction with R0\nstill requested and triggers the \"callback unexpected regs\" verifier bug.\nA CAP_BPF task can therefore cause a WARN and an -EFAULT BPF_PROG_LOAD.\n\nTail calls reachable from callbacks are already rejected later by\ncheck_max_stack_depth(). Reject a tail call made directly by a callback\nbefore constructing the inconsistent return state, using the existing\ndiagnostic. Tail calls from ordinary subprograms keep their current\nbehavior.",
"id": "GHSA-3q38-vxgf-8598",
"modified": "2026-09-25T12:31:35Z",
"published": "2026-09-25T12:31:35Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98061"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/266aa4ad0b2e82397cd9045752c9bff03d98eddd"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/617c8266e49f45747f71e74177646a63f72b7025"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/96d31b28263c429a56e4de85bcf744a5c320b3a3"
}
],
"schema_version": "1.4.0",
"severity": []
}
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