FKIE_CVE-2026-98134

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: check_cond_jmp_op(): properly infer if register is null Nicholas Carlini reported a bug when verifier can incorrectly infer that a pointer is non-null. The bug occurs when two pointers are compared and one of them has a type w/o PTR_MAYBE_NULL flag, but which allows a value to be NULL at runtime. Here is an example: // `a` is PTR_TO_MEM | MEM_RDONLY | PTR_UNTRUSTED // `a` is 0 at runtime. // `b` is PTR_TO_MAP_VALUE | PTR_MAYBE_NULL void *a = bpf_rdonly_cast(0, 0); int *b = bpf_map_lookup_elem(...); if (a == b) *b = 42; // verifier does not catch null pointer dereference This happens because of a special case in check_cond_jmp_op(), which attempts to strip PTR_MAYBE_NULL flags from pointer types, when processing comparisons like `rA == rB`, if either rA or rB can't be null. The non-null property is derived based on the absence of PTR_MAYBE_NULL flag on rA's or rB's type. But that is not sufficient for types like PTR_TO_MEM, as in the example. This patch replaces type_may_be_null() call with reg_not_null(), which contains an allowlist of types for which absence of PTR_MAYBE_NULL actually means that the value can't be NULL at runtime. At the moment, the list in the reg_not_null() omits two types for which PTR_MAYBE_NULL is applicable: PTR_TO_XDP_SOCK and PTR_TO_BUF. In order to remain backward compatible, and assuming that only comparison between pointers of the same type makes sense, this commit extends reg_not_null(). W/o such an extension e.g. verifier_jeq_infer_not_null/null_ptr_to_map_value fails. reg_not_null() can be extended further, but I deem that out of scope for the fix at hand. Explicit base_type(...) != PTR_TO_BTF_ID checks in the check_cond_jmp_op() can be removed with migration to reg_not_null(), but that is a behavioural change, as the special case would start matching for PTR_TO_BTF_ID that is also is_trusted_reg(). I omit the behavioural change from this commit.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/b55c9f019e169ed0d01394f96e172286a8b21b99
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/d3ef6c097ba078e1f8c7239d76a0ce8b61e75095
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": "b55c9f019e169ed0d01394f96e172286a8b21b99",
              "status": "affected",
              "version": "befae75856ab406a3f3fab2aa2118cf3b2dfe3e6",
              "versionType": "git"
            },
            {
              "lessThan": "d3ef6c097ba078e1f8c7239d76a0ce8b61e75095",
              "status": "affected",
              "version": "befae75856ab406a3f3fab2aa2118cf3b2dfe3e6",
              "versionType": "git"
            }
          ]
        },
        {
          "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": "6.2"
            },
            {
              "lessThan": "6.2",
              "status": "unaffected",
              "version": "0",
              "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: check_cond_jmp_op(): properly infer if register is null\n\nNicholas Carlini reported a bug when verifier can incorrectly infer\nthat a pointer is non-null. The bug occurs when two pointers are\ncompared and one of them has a type w/o PTR_MAYBE_NULL flag,\nbut which allows a value to be NULL at runtime.\nHere is an example:\n\n  // `a` is PTR_TO_MEM | MEM_RDONLY | PTR_UNTRUSTED\n  // `a` is 0 at runtime.\n  // `b` is PTR_TO_MAP_VALUE | PTR_MAYBE_NULL\n  void *a = bpf_rdonly_cast(0, 0);\n  int  *b = bpf_map_lookup_elem(...);\n\n  if (a == b)\n    *b = 42;  // verifier does not catch null pointer dereference\n\nThis happens because of a special case in check_cond_jmp_op(),\nwhich attempts to strip PTR_MAYBE_NULL flags from pointer types,\nwhen processing comparisons like `rA == rB`, if either rA or rB can\u0027t\nbe null.\n\nThe non-null property is derived based on the absence of\nPTR_MAYBE_NULL flag on rA\u0027s or rB\u0027s type. But that is not sufficient\nfor types like PTR_TO_MEM, as in the example.\n\nThis patch replaces type_may_be_null() call with reg_not_null(),\nwhich contains an allowlist of types for which absence of\nPTR_MAYBE_NULL actually means that the value can\u0027t be NULL at runtime.\n\nAt the moment, the list in the reg_not_null() omits two types for\nwhich PTR_MAYBE_NULL is applicable: PTR_TO_XDP_SOCK and PTR_TO_BUF.\nIn order to remain backward compatible, and assuming that only\ncomparison between pointers of the same type makes sense,\nthis commit extends reg_not_null(). W/o such an extension e.g.\nverifier_jeq_infer_not_null/null_ptr_to_map_value fails.\n\nreg_not_null() can be extended further, but I deem that out of scope\nfor the fix at hand. Explicit base_type(...) != PTR_TO_BTF_ID\nchecks in the check_cond_jmp_op() can be removed with migration to\nreg_not_null(), but that is a behavioural change, as the special case\nwould start matching for PTR_TO_BTF_ID that is also is_trusted_reg().\nI omit the behavioural change from this commit."
    }
  ],
  "id": "CVE-2026-98134",
  "lastModified": "2026-09-25T11:17:44.820",
  "metrics": {},
  "published": "2026-09-25T11:17:44.820",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/b55c9f019e169ed0d01394f96e172286a8b21b99"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/d3ef6c097ba078e1f8c7239d76a0ce8b61e75095"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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