bpf: Mark the zero register precise for a register-form NULL check

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Summary

CVECVE-2026-98040
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-25 11:17:32 UTC
Updated2026-10-19 10:17:57 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: bpf: Mark the zero register precise for a register-form NULL check check_cond_jmp_op() accepts "if rA <op> rB" as a NULL check for a nullable pointer rA when rB is a scalar known to be zero, lifts PTR_MAYBE_NULL from rA in the corresponding branch and does not mark rB precise. Consider the following program: r0 = bpf_get_prandom_u32(); r6 = 1; /* the r6 == 0 path is explored first */ if (r0 == 0) goto 1f; r6 = 0; 1: r0 = bpf_map_lookup_elem(map, &0); /* absent, NULL at runtime */ if (r0 == r6) goto 2f; /* taken as a NULL check for r0 */ *(u8 *)(r0 + 0); /* verifier: map value; runtime: zero */ 2: return 0; The r6 == 0 path is explored first and the dereference is accepted. The r6 == 1 path is pruned at the checkpoint recorded for (1), so the comparison is never verified with a non-zero r6. At runtime a failed lookup returns NULL, NULL != 1 takes the non-NULL edge and the program dereferences a pointer that is zero.

Risk And Classification

EPSS: 0.001890000 probability, percentile 0.076630000 (date 2026-09-27)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 2f4cb53eed448c1aeb6f4b40cf9c810716d8218c ddca9a3b8833168dda3e62676648a636fb3f221c git Not specified
CNA Linux Linux affected 2f4cb53eed448c1aeb6f4b40cf9c810716d8218c 6aed0134d3cda6382385a734ae0158eb7df6b142 git Not specified
CNA Linux Linux affected 7.1 Not specified
CNA Linux Linux unaffected 7.1 semver Not specified
CNA Linux Linux unaffected 7.2.7 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/ddca9a3b8833168dda3e62676648a636fb3f221c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/6aed0134d3cda6382385a734ae0158eb7df6b142 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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