Linux Kernel BPF Interp sdiv/smod Undefined Behavior
CVE-2026-31525 Published on April 22, 2026
bpf: Fix undefined behavior in interpreter sdiv/smod for INT_MIN
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().
Products Associated with CVE-2026-31525
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Affected Versions
Linux:- Version ec0e2da95f72d4a46050a4d994e4fe471474fd80 and below 694ea55f1b1c74f9942d91ec366ae9e822422e42 is affected.
- Version ec0e2da95f72d4a46050a4d994e4fe471474fd80 and below 9ab1227765c446942f290c83382f0b19887c55cf is affected.
- Version ec0e2da95f72d4a46050a4d994e4fe471474fd80 and below f14ca604c0ff274fba19f73f1f0485c0047c1396 is affected.
- Version ec0e2da95f72d4a46050a4d994e4fe471474fd80 and below 0d5d8c3ce45c734aaf3c51cbef59155a6746157d is affected.
- Version ec0e2da95f72d4a46050a4d994e4fe471474fd80 and below c77b30bd1dcb61f66c640ff7d2757816210c7cb0 is affected.
- Version 6.6 is affected.
- Before 6.6 is unaffected.
- Version 6.6.131, <= 6.6.* is unaffected.
- Version 6.12.80, <= 6.12.* is unaffected.
- Version 6.18.21, <= 6.18.* is unaffected.
- Version 6.19.11, <= 6.19.* is unaffected.
- Version 7.0, <= * is unaffected.