CVE-2026-43455

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

mctp: route: hold key->lock in mctp_flow_prepare_output()

mctp_flow_prepare_output() checks key->dev and may call mctp_dev_set_key(), but it does not hold key->lock while doing so.

mctp_dev_set_key() and mctp_dev_release_key() are annotated with __must_hold(&key->lock), so key->dev access is intended to be serialized by key->lock. The mctp_sendmsg() transmit path reaches mctp_flow_prepare_output() via mctp_local_output() -> mctp_dst_output() without holding key->lock, so the check-and-set sequence is racy.

Example interleaving:

CPU0 CPU1

mctp_flow_prepare_output(key, devA) if (!key->dev) // sees NULL mctp_flow_prepare_output( key, devB) if (!key->dev) // still NULL mctp_dev_set_key(devB, key) mctp_dev_hold(devB) key->dev = devB mctp_dev_set_key(devA, key) mctp_dev_hold(devA) key->dev = devA // overwrites devB

Now both devA and devB references were acquired, but only the final key->dev value is tracked for release. One reference can be lost, causing a resource leak as mctp_dev_release_key() would only decrease the reference on one dev.

Fix by taking key->lock around the key->dev check and mctp_dev_set_key() call.

Affected Software

References

• https://git.kernel.org/stable/c/0695712f3a6f1a48915f95767cfb42077683dcdc
• https://git.kernel.org/stable/c/47893166bc5611ee9a20de6b8d2933b2320fb772
• https://git.kernel.org/stable/c/7d86aa41c073c4e7eb75fd2e674f1fd8f289728a
• https://git.kernel.org/stable/c/86f5334fcb48a5b611c33364ab52ca684d0f6d91
• https://git.kernel.org/stable/c/8d27d9b260dd19c1b519e1a13de6448f9984e30e
• https://git.kernel.org/stable/c/925a5ffd99cddd7a7e41d5ad120c7a2c6d50260f