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

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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.

Fixes: 0a3a809089 ("net/tcp: Verify inbound TCP-AO signed segments")
Cc: stable@vger.kernel.org
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Link: https://patch.msgid.link/aoIriv3pHDgII2YR@v4bel
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Hyunwoo Kim 2026-08-17 06:28:42 +09:00 committed by Jakub Kicinski
parent 8e2efb3f45
commit da4471557f
1 changed files with 9 additions and 0 deletions
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9
net/ipv4/tcp_ao.c
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@ -1160,6 +1160,15 @@ void tcp_ao_connect_init(struct sock *sk)
l3index = l3mdev_master_ifindex_by_index(sock_net(sk),
sk->sk_bound_dev_if);
hlist_for_each_entry(key, &ao_info->head, node) {
if (tcp_ao_key_cmp(key, l3index, addr, key->prefixlen,
family, -1, -1)) {
/* pairs with tcp_inbound_ao_hash() */
synchronize_rcu();
break;
}
}
hlist_for_each_entry_safe(key, next, &ao_info->head, node) {
if (!tcp_ao_key_cmp(key, l3index, addr, key->prefixlen, family, -1, -1))
continue;