| Message ID | 135fda25-22d5-837a-782b-ceee50e19844@ya.ru (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 3ff8bff704f4de125dca2262e5b5b963a3da1d87 |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net,v3] unix: Fix race in SOCK_SEQPACKET's unix_dgram_sendmsg() | expand |
Hello: This patch was applied to netdev/net.git (master) by Paolo Abeni <pabeni@redhat.com>: On Tue, 13 Dec 2022 00:05:53 +0300 you wrote: > 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 > > [...] Here is the summary with links: - [net,v3] unix: Fix race in SOCK_SEQPACKET's unix_dgram_sendmsg() https://git.kernel.org/netdev/net/c/3ff8bff704f4 You are awesome, thank you!
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;
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 <tkhai@ya.ru> --- v3: Return to v1 variant. It looks very bad to return special retval in case of race in kernel, when userspace can't control this. It looks bad to introduce corner case optimization, which normally occurs almost never. net/unix/af_unix.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)