Medium [CVE-2026-68462] Reject negative const offsets for buffer pointers
This medium-severity Red Hat Linux advisory covers CVE-2026-68462.
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Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: Reject negative const offsets for buffer pointers The verifier rejects variable offsets for PTR_TO_TP_BUFFER and PTR_TO_BUF accesses, but it currently accepts a constant negative offset produced by pointer arithmetic.
Commit 022ac0750883 ("bpf: use reg->var_off instead of reg->off for pointers") moved constant pointer offsets from reg->off to reg->var_off. However, __check_buffer_access() continued to check only the instruction offset.
An access with reg->var_off equal to -8 and an instruction offset of zero therefore passes verification. For writable raw tracepoints, the access end is also calculated from the unsigned reg->var_off.value.
An eight-byte access starting at -8 wraps the calculated end to zero, allowing the program to load and attach without increasing max_tp_access. After ensuring that reg->var_off is constant, calculate the effective access start using signed arithmetic and reject it when it is negative.
Use the validated start to calculate the access end for both PTR_TO_TP_BUFFER and PTR_TO_BUF. The BPF (Berkeley Packet Filter) verifier, responsible for ensuring the safety of BPF programs, incorrectly processed negative constant offsets when accessing buffer pointers.
This oversight could allow a local attacker to craft a malicious BPF program that bypasses memory access restrictions.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 25 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 25 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 25 days ago·verify at source
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