From 3ff8bff704f4de125dca2262e5b5b963a3da1d87 Mon Sep 17 00:00:00 2001 From: Kirill Tkhai Date: Tue, 13 Dec 2022 00:05:53 +0300 Subject: unix: Fix race in SOCK_SEQPACKET's unix_dgram_sendmsg() There is a race resulting in alive SOCK_SEQPACKET socket may change its state from TCP_ESTABLISHED to TCP_CLOSE: unix_release_sock(peer) unix_dgram_sendmsg(sk) sock_orphan(peer) sock_set_flag(peer, SOCK_DEAD) sock_alloc_send_pskb() if !(sk->sk_shutdown & SEND_SHUTDOWN) OK if sock_flag(peer, SOCK_DEAD) sk->sk_state = TCP_CLOSE sk->sk_shutdown = SHUTDOWN_MASK After that socket sk remains almost normal: it is able to connect, listen, accept and recvmsg, while it can't sendmsg. Since this is the only possibility for alive SOCK_SEQPACKET to change the state in such way, we should better fix this strange and potentially danger corner case. Note, that we will return EPIPE here like this is normally done in sock_alloc_send_pskb(). Originally used ECONNREFUSED looks strange, since it's strange to return a specific retval in dependence of race in kernel, when user can't affect on this. Also, move TCP_CLOSE assignment for SOCK_DGRAM sockets under state lock to fix race with unix_dgram_connect(): unix_dgram_connect(other) unix_dgram_sendmsg(sk) unix_peer(sk) = NULL unix_state_unlock(sk) unix_state_double_lock(sk, other) sk->sk_state = TCP_ESTABLISHED unix_peer(sk) = other unix_state_double_unlock(sk, other) sk->sk_state = TCP_CLOSED This patch fixes both of these races. Fixes: 83301b5367a9 ("af_unix: Set TCP_ESTABLISHED for datagram sockets too") Signed-off-by: Kirill Tkhai Link: https://lore.kernel.org/r/135fda25-22d5-837a-782b-ceee50e19844@ya.ru Signed-off-by: Paolo Abeni --- net/unix/af_unix.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) (limited to 'net/unix/af_unix.c') diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index ede2b2a140a4..f0c2293f1d3b 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -1999,13 +1999,20 @@ restart_locked: unix_state_lock(sk); err = 0; - if (unix_peer(sk) == other) { + if (sk->sk_type == SOCK_SEQPACKET) { + /* We are here only when racing with unix_release_sock() + * is clearing @other. Never change state to TCP_CLOSE + * unlike SOCK_DGRAM wants. + */ + unix_state_unlock(sk); + err = -EPIPE; + } else if (unix_peer(sk) == other) { unix_peer(sk) = NULL; unix_dgram_peer_wake_disconnect_wakeup(sk, other); + sk->sk_state = TCP_CLOSE; unix_state_unlock(sk); - sk->sk_state = TCP_CLOSE; unix_dgram_disconnected(sk, other); sock_put(other); err = -ECONNREFUSED; -- cgit v1.2.3