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Message-ID: <38a920a7-cfba-7929-886d-c3c6effc0c43@ya.ru>
Date: Sun, 20 Nov 2022 02:16:47 +0300
From: Kirill Tkhai <tkhai@...ru>
To: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
pabeni@...hat.com, netdev@...r.kernel.org, tkhai@...ru
Subject: [PATCH net] 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.
Also, move TCP_CLOSE assignment for SOCK_DGRAM sockets under state lock.
Signed-off-by: Kirill Tkhai <tkhai@...ru>
---
net/unix/af_unix.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index b3545fc68097..6fd745cfc492 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1999,13 +1999,20 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
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;
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