Bug 2460672 (CVE-2026-31525)

Summary: CVE-2026-31525 kernel: bpf: Fix undefined behavior in interpreter sdiv/smod for INT_MIN
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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OS: Linux   
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A flaw was found in the Linux kernel's Berkeley Packet Filter (BPF) interpreter. The interpreter's signed 32-bit division and modulo operations exhibit undefined behavior when processing the minimum 32-bit signed integer value (S32_MIN) due to an incorrect use of the `abs()` macro. This inconsistency between the interpreter's execution and the verifier's expected behavior can be leveraged by a local attacker. Successful exploitation could lead to out-of-bounds memory access within BPF maps, potentially resulting in information disclosure or privilege escalation.
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Description OSIDB Bzimport 2026-04-22 15:04:33 UTC 
In the Linux kernel, the following vulnerability has been resolved:

bpf: Fix undefined behavior in interpreter sdiv/smod for INT_MIN

The BPF interpreter's signed 32-bit division and modulo handlers use
the kernel abs() macro on s32 operands. The abs() macro documentation
(include/linux/math.h) explicitly states the result is undefined when
the input is the type minimum. When DST contains S32_MIN (0x80000000),
abs((s32)DST) triggers undefined behavior and returns S32_MIN unchanged
on arm64/x86. This value is then sign-extended to u64 as
0xFFFFFFFF80000000, causing do_div() to compute the wrong result.

The verifier's abstract interpretation (scalar32_min_max_sdiv) computes
the mathematically correct result for range tracking, creating a
verifier/interpreter mismatch that can be exploited for out-of-bounds
map value access.

Introduce abs_s32() which handles S32_MIN correctly by casting to u32
before negating, avoiding signed overflow entirely. Replace all 8
abs((s32)...) call sites in the interpreter's sdiv32/smod32 handlers.

s32 is the only affected case -- the s64 division/modulo handlers do
not use abs().
Comment 1 Keith Grant 2026-04-22 20:23:06 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026042213-CVE-2026-31525-0fff@gregkh/T