Bug 2461519 (CVE-2026-31657)

Summary: CVE-2026-31657 kernel: batman-adv: hold claim backbone gateways by reference
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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Doc Text:
A flaw was found in the Linux kernel's batman-adv component. The batadv_bla_add_claim() function can improperly drop a reference to a backbone gateway while other parts of the code, such as the netlink claim dump path, still hold and attempt to use a pointer to the freed memory. This creates a use-after-free vulnerability, which could allow a local attacker to cause system instability or a denial of service (DoS).
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Description OSIDB Bzimport 2026-04-24 15:06:14 UTC 
In the Linux kernel, the following vulnerability has been resolved:

batman-adv: hold claim backbone gateways by reference

batadv_bla_add_claim() can replace claim->backbone_gw and drop the old
gateway's last reference while readers still follow the pointer.

The netlink claim dump path dereferences claim->backbone_gw->orig and
takes claim->backbone_gw->crc_lock without pinning the underlying
backbone gateway. batadv_bla_check_claim() still has the same naked
pointer access pattern.

Reuse batadv_bla_claim_get_backbone_gw() in both readers so they operate
on a stable gateway reference until the read-side work is complete.
This keeps the dump and claim-check paths aligned with the lifetime
rules introduced for the other BLA claim readers.
Comment 1 Keith Grant 2026-04-24 22:09:41 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026042402-CVE-2026-31657-fbab@gregkh/T