CVE-2026-80849

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

net/tcp-ao: fix use-after-free of current_key on reconnect to another peer

tcp_inbound_ao_hash() is called before bh_lock_sock_nested() is taken,

with only rcu_read_lock() held. On the fast path for established

sockets, if the rnext_keyid sent by the peer differs from

current_key->sndid, the key the peer asked for is looked up and stored

in current_key. The lookup is inside the RCU read side, but current_key

outlives it.

When the socket is disconnected and connect() is called again for

another peer, tcp_ao_connect_init() unlinks every key that does not

match the new peer and frees it with call_rcu(). If current_key points

at such a key, it is cleared to NULL.

The fast path reads sk_state only once on entry, so a softirq that got

into it while the socket was still established can update current_key

after that loop has already run. The update is inside the RCU read side,

so it comes before the call_rcu() callback, and once the callback frees

the key, current_key is left pointing at freed memory.

The next transmission picks that pointer up in tcp_get_current_key().

tcp_ao_transmit_skb() then reads the traffic key from the freed object,

which is the use-after-free.

Wait for one grace period before unlinking, and only if a key is going

to be removed. By the time tcp_connect() runs the socket is already in

TCP_SYN_SENT, and TCP_AO_ESTABLISHED does not contain TCPF_SYN_SENT, so

a softirq entering after the wait cannot reach the fast path, and the

ones already in it have finished. The existing NULL handling in the loop

is then enough.