FKIE_CVE-2026-98061

Vulnerability from fkie_nvd - Published: 2026-09-25 11:17 - Updated: 2026-09-25 11:17
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
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/266aa4ad0b2e82397cd9045752c9bff03d98eddd
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/617c8266e49f45747f71e74177646a63f72b7025
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/96d31b28263c429a56e4de85bcf744a5c320b3a3
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "kernel/bpf/verifier.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "617c8266e49f45747f71e74177646a63f72b7025",
              "status": "affected",
              "version": "a6c22c91b6284e4713c0cf5b20ab3c9c71b77ae8",
              "versionType": "git"
            },
            {
              "lessThan": "96d31b28263c429a56e4de85bcf744a5c320b3a3",
              "status": "affected",
              "version": "e3245f8990431950d20631c72236d4e8cb2dcde8",
              "versionType": "git"
            },
            {
              "lessThan": "266aa4ad0b2e82397cd9045752c9bff03d98eddd",
              "status": "affected",
              "version": "e3245f8990431950d20631c72236d4e8cb2dcde8",
              "versionType": "git"
            },
            {
              "lessThan": "6.18.53",
              "status": "affected",
              "version": "6.18.2",
              "versionType": "semver"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "kernel/bpf/verifier.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.19"
            },
            {
              "lessThan": "6.19",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.53",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.7",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3-rc2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "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."
    }
  ],
  "id": "CVE-2026-98061",
  "lastModified": "2026-09-25T11:17:35.110",
  "metrics": {},
  "published": "2026-09-25T11:17:35.110",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/266aa4ad0b2e82397cd9045752c9bff03d98eddd"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/617c8266e49f45747f71e74177646a63f72b7025"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/96d31b28263c429a56e4de85bcf744a5c320b3a3"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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