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

Overview

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.

Affected

• Linux >= 0a3a809089eb1d4a0a2fd0c16b520d603988c859 < 84a93b4e012587d0a4a84ffb23ec6da18e9d85f9
• Linux >= 0a3a809089eb1d4a0a2fd0c16b520d603988c859 < 73fde8fe4469f4ed8f0afcc0b9d6413002a9e6b3
• Linux >= 0a3a809089eb1d4a0a2fd0c16b520d603988c859 < e54ad693eddb40c595add013f545354c538e325b
• Linux >= 0a3a809089eb1d4a0a2fd0c16b520d603988c859 < 2857dcbd03cf3354af0fba1b65c6a260fb43811a
• Linux >= 0a3a809089eb1d4a0a2fd0c16b520d603988c859 < da4471557f279d0f56605158a625bb6e49ef7d41
• Linux 6.7

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.