Bug 2492322 (CVE-2026-53081)

Summary: CVE-2026-53081 kernel: bpf: Enforce regsafe base id consistency for BPF_ADD_CONST scalars
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's Berkeley Packet Filter (BPF) verifier. This vulnerability occurs due to inconsistent base ID mapping when the `regsafe()` function compares scalar registers with `BPF_ADD_CONST` values. This inconsistency allows the BPF verifier to incorrectly succeed in state pruning, which could enable a bypass of its security mechanisms. Such a bypass may lead to unexpected system behavior or potentially allow an attacker to execute unauthorized operations.
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Description OSIDB Bzimport 2026-06-24 18:05:40 UTC 
In the Linux kernel, the following vulnerability has been resolved:

bpf: Enforce regsafe base id consistency for BPF_ADD_CONST scalars

When regsafe() compares two scalar registers that both carry
BPF_ADD_CONST, check_scalar_ids() maps their full compound id
(aka base | BPF_ADD_CONST flag) as one idmap entry. However,
it never verifies that the underlying base ids, that is, with
the flag stripped are consistent with existing idmap mappings.

This allows construction of two verifier states where the old
state has R3 = R2 + 10 (both sharing base id A) while the current
state has R3 = R4 + 10 (base id C, unrelated to R2). The idmap
creates two independent entries: A->B (for R2) and A|flag->C|flag
(for R3), without catching that A->C conflicts with A->B. State
pruning then incorrectly succeeds.

Fix this by additionally verifying base ID mapping consistency
whenever BPF_ADD_CONST is set: after mapping the compound ids,
also invoke check_ids() on the base IDs (flag bits stripped).
This ensures that if A was already mapped to B from comparing
the source register, any ADD_CONST derivative must also derive
from B, not an unrelated C.
Comment 1 Keith Grant 2026-06-26 17:58:16 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026062407-CVE-2026-53081-4676@gregkh/T