Bug 2457626 (CVE-2026-31413)

Summary: CVE-2026-31413 kernel: bpf: Fix unsound scalar forking in maybe_fork_scalars() for BPF_OR
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: unspecifiedKeywords: Security
Target Milestone: ---   
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in the Linux kernel's Berkeley Packet Filter (BPF) component. This vulnerability arises from an incorrect handling of certain operations within the BPF verifier, which is responsible for ensuring the safety of BPF programs. This discrepancy between the verifier's analysis and the program's actual execution can be exploited by a local attacker. Successful exploitation could lead to out-of-bounds memory access, potentially allowing for privilege escalation or information disclosure.
 Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-04-12 07:01:17 UTC 
In the Linux kernel, the following vulnerability has been resolved:

bpf: Fix unsound scalar forking in maybe_fork_scalars() for BPF_OR

maybe_fork_scalars() is called for both BPF_AND and BPF_OR when the
source operand is a constant.  When dst has signed range [-1, 0], it
forks the verifier state: the pushed path gets dst = 0, the current
path gets dst = -1.

For BPF_AND this is correct: 0 & K == 0.
For BPF_OR this is wrong:    0 | K == K, not 0.

The pushed path therefore tracks dst as 0 when the runtime value is K,
producing an exploitable verifier/runtime divergence that allows
out-of-bounds map access.

Fix this by passing env->insn_idx (instead of env->insn_idx + 1) to
push_stack(), so the pushed path re-executes the ALU instruction with
dst = 0 and naturally computes the correct result for any opcode.
Comment 1 Alexander B 2026-04-13 09:06:35 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026041220-CVE-2026-31413-cce6@gregkh/T