{"id":"CVE-2026-98134","state":"PUBLISHED","title":"bpf: check_cond_jmp_op(): properly infer if register is null","description":"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't\nbe null.\n\nThe non-null property is derived based on the absence of\nPTR_MAYBE_NULL flag on rA's or rB's 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't 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.","publishedAt":"2026-09-25T10:36:12.919Z","updatedAt":"2026-10-21T12:54:40.601Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"befae75856ab406a3f3fab2aa2118cf3b2dfe3e6","status":"affected","lessThan":"d51cd486930f5bcfd4b55d55ab8e47b03f93d2ed","versionType":"git"},{"version":"befae75856ab406a3f3fab2aa2118cf3b2dfe3e6","status":"affected","lessThan":"dfd8f8adda565e08c370c45cf9d6b2511ba9b5c6","versionType":"git"},{"version":"befae75856ab406a3f3fab2aa2118cf3b2dfe3e6","status":"affected","lessThan":"9bf96b4347f541604b3caadeabda0773d9ceaf2a","versionType":"git"},{"version":"befae75856ab406a3f3fab2aa2118cf3b2dfe3e6","status":"affected","lessThan":"b55c9f019e169ed0d01394f96e172286a8b21b99","versionType":"git"},{"version":"befae75856ab406a3f3fab2aa2118cf3b2dfe3e6","status":"affected","lessThan":"d3ef6c097ba078e1f8c7239d76a0ce8b61e75095","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/verifier.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.2","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.2","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.7","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/verifier.c"]}],"references":["https://git.kernel.org/stable/c/d51cd486930f5bcfd4b55d55ab8e47b03f93d2ed","https://git.kernel.org/stable/c/dfd8f8adda565e08c370c45cf9d6b2511ba9b5c6","https://git.kernel.org/stable/c/9bf96b4347f541604b3caadeabda0773d9ceaf2a","https://git.kernel.org/stable/c/b55c9f019e169ed0d01394f96e172286a8b21b99","https://git.kernel.org/stable/c/d3ef6c097ba078e1f8c7239d76a0ce8b61e75095"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:43.249Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/98xxx/CVE-2026-98134.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-98134","state":"PUBLISHED","datePublished":"2026-09-25T10:36:12.919Z","dateUpdated":"2026-10-21T12:54:40.601Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:25:14.319Z"},"containers":{"cna":{"title":"bpf: check_cond_jmp_op(): properly infer if register is null","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't\nbe null.\n\nThe non-null property is derived based on the absence of\nPTR_MAYBE_NULL flag on rA's or rB's 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't 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."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"befae75856ab406a3f3fab2aa2118cf3b2dfe3e6","status":"affected","lessThan":"d51cd486930f5bcfd4b55d55ab8e47b03f93d2ed","versionType":"git"},{"version":"befae75856ab406a3f3fab2aa2118cf3b2dfe3e6","status":"affected","lessThan":"dfd8f8adda565e08c370c45cf9d6b2511ba9b5c6","versionType":"git"},{"version":"befae75856ab406a3f3fab2aa2118cf3b2dfe3e6","status":"affected","lessThan":"9bf96b4347f541604b3caadeabda0773d9ceaf2a","versionType":"git"},{"version":"befae75856ab406a3f3fab2aa2118cf3b2dfe3e6","status":"affected","lessThan":"b55c9f019e169ed0d01394f96e172286a8b21b99","versionType":"git"},{"version":"befae75856ab406a3f3fab2aa2118cf3b2dfe3e6","status":"affected","lessThan":"d3ef6c097ba078e1f8c7239d76a0ce8b61e75095","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/verifier.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.2","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.2","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.114","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.57","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.7","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/bpf/verifier.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/d51cd486930f5bcfd4b55d55ab8e47b03f93d2ed"},{"url":"https://git.kernel.org/stable/c/dfd8f8adda565e08c370c45cf9d6b2511ba9b5c6"},{"url":"https://git.kernel.org/stable/c/9bf96b4347f541604b3caadeabda0773d9ceaf2a"},{"url":"https://git.kernel.org/stable/c/b55c9f019e169ed0d01394f96e172286a8b21b99"},{"url":"https://git.kernel.org/stable/c/d3ef6c097ba078e1f8c7239d76a0ce8b61e75095"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-21T12:54:40.601Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.2","versionEndExcluding":"6.6.160"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.2","versionEndExcluding":"6.12.114"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.2","versionEndExcluding":"6.18.57"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.2","versionEndExcluding":"7.2.7"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.2","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}