CVE-2026-98061 (GCVE-0-2026-98061)
Vulnerability from cvelistv5
Published
2026-09-25 10:24
Modified
2026-10-19 09:13
Severity ?
Summary
In 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.
References
Impacted products
Vendor Product Version
Linux Linux Version: a6c22c91b6284e4713c0cf5b20ab3c9c71b77ae8
Version: e3245f8990431950d20631c72236d4e8cb2dcde8
Version: e3245f8990431950d20631c72236d4e8cb2dcde8
Version: 6.18.2   ≤
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          "defaultStatus": "unaffected",
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          "programFiles": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:13:09.930Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
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          "url": "https://git.kernel.org/stable/c/617c8266e49f45747f71e74177646a63f72b7025"
        },
        {
          "url": "https://git.kernel.org/stable/c/96d31b28263c429a56e4de85bcf744a5c320b3a3"
        },
        {
          "url": "https://git.kernel.org/stable/c/266aa4ad0b2e82397cd9045752c9bff03d98eddd"
        }
      ],
      "title": "bpf: Reject tail calls directly from callback frames",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98061",
    "datePublished": "2026-09-25T10:24:06.001Z",
    "dateReserved": "2026-09-25T10:19:56.073Z",
    "dateUpdated": "2026-10-19T09:13:09.930Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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