bpf: check_cond_jmp_op(): properly infer if register is null

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-98134
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-25 11:17:44 UTC
Updated2026-09-30 14:10:59 UTC
DescriptionIn 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.

Risk And Classification

EPSS: 0.001560000 probability, percentile 0.040350000 (date 2026-09-27)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected befae75856ab406a3f3fab2aa2118cf3b2dfe3e6 b55c9f019e169ed0d01394f96e172286a8b21b99 git Not specified
CNA Linux Linux affected befae75856ab406a3f3fab2aa2118cf3b2dfe3e6 d3ef6c097ba078e1f8c7239d76a0ce8b61e75095 git Not specified
CNA Linux Linux affected 6.2 Not specified
CNA Linux Linux unaffected 6.2 semver Not specified
CNA Linux Linux unaffected 7.2.7 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc2 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/d3ef6c097ba078e1f8c7239d76a0ce8b61e75095 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/b55c9f019e169ed0d01394f96e172286a8b21b99 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

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