CVE-2026-64095

Summary

In the Linux kernel, the following vulnerability has been resolved:

batman-adv: bla: avoid double decrement of bla.num_requests

The bla.num_requests is increased when no request_sent was in progress. And it is decremented in various places (announcement was received, backbone is purged, periodic work). But the check if the request_sent is actually set to a specific state and the atomic_dec/_inc are not safe because they are not atomic (TOCTOU) and multiple such code portions can run concurrently.

At the same time, it is necessary to modify request_sent (state) and bla.num_requests atomically. Otherwise batadv_bla_send_request() might set request_sent to 1 and is interrupted. batadv_handle_announce() can then set request_sent back to 0 and decrement num_requests before batadv_bla_send_request() incremented it.

The two operations must therefore be locked. And since state (request_sent) and wait_periods are only accessed inside this lock, they can be converted to simpler datatypes. And to avoid that the bla.num_requests is touched by a parallel running context with a valid backbone_gw reference after batadv_bla_purge_backbone_gw() ran, a third state "stopped" is required to correctly signal that a backbone_gw is in the state of being cleaned up.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/1f013bc94154f2e78e97d0296175664224c796e0
• https://git.kernel.org/stable/c/5328b95960774f2e189f22485616bc7b8eb2f7e3
• https://git.kernel.org/stable/c/8ff9c59d1b7b48c2596878341a5310f32895d52b
• https://git.kernel.org/stable/c/a9393751ecf7e9096f93cb6eed02db4f79125765
• https://git.kernel.org/stable/c/461f1e3dfb888701895b766446c55db2b10db705
• https://git.kernel.org/stable/c/45384612f29692fbf0c770200361a7acff90125c
• https://git.kernel.org/stable/c/65497ad155a3246df177b5ef662cd6e5a32cb470
• https://git.kernel.org/stable/c/83ab69bd12b80f6ea169c8bea6977701b53a043d

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