CVE-2026-74696tcp: fix TFO max_qlen accounting across reuseport migration

Official description

In the Linux kernel, the following vulnerability has been resolved: tcp: fix TFO max_qlen accounting across reuseport migration A listener's TCP_FASTOPEN max_qlen stops being accurate and lets through far more pending Fast Open requests than it was configured for. This only shows up with SO_REUSEPORT listener migration, where closing a listener hands its still-pending TFO children over to a surviving one. fastopenq.qlen is charged in tcp_fastopen_create_child() when the child is created and uncharged in reqsk_fastopen_remove() when the handshake completes. The uncharge follows rsk_listener of the request the child points at, and inet_reqsk_clone() has repointed the child at a new request owned by the new listener, so the ++ and the -- land on two different sockets. The new listener's qlen drifts negative and its limit no longer binds. Charge the new listener during migration, like reqsk_queue_migrated() already does for queue->young and queue->qlen.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/e98f0d80b9cccb5f828425d2004f9686e7d1ae24
• https://git.kernel.org/stable/c/b6247e0f96bd825ffb2005257f6177b5e642dee6
• https://git.kernel.org/stable/c/585fc5247d14939a561056aa2addd9b7c2b1f670
• https://git.kernel.org/stable/c/6e10ee56524a26b250229ad348637825646ddb88
• https://git.kernel.org/stable/c/a66e869cf0c90c1e47ae75f72b6482acbfc808ff
• https://git.kernel.org/stable/c/d974618b2097453778389d385e3741629c40e0a3
• https://git.kernel.org/stable/c/a0ab2ba83e35159d81cec830a92e885ecf8139be