net/smc: restrict non-blocking connect finish

The smc_poll code tries to finish connect() if the socket is in
state SMC_INIT and polling of the internal CLC-socket returns with
EPOLLOUT. This makes sense for a select/poll call following a connect
call, but not without preceding connect().
With this patch smc_poll starts connect logic only, if the CLC-socket
is no longer in its initial state TCP_CLOSE.

In addition, a poll error on the internal CLC-socket is always
propagated to the SMC socket.

With this patch the code path mentioned by syzbot
https://syzkaller.appspot.com/bug?extid=03faa2dc16b8b64be396
is no longer possible.

Signed-off-by: Ursula Braun <ubraun@linux.ibm.com>
Reported-by: syzbot+03faa2dc16b8b64be396@syzkaller.appspotmail.com
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 6 deletions

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 4470501374bf..8b4c059bd13b 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -1166,13 +1166,15 @@ static __poll_t smc_poll(struct file *file, struct socket *sock,
                 /* delegate to CLC child sock */
                 release_sock(sk);
                 mask = smc->clcsock->ops->poll(file, smc->clcsock, wait);
-                /* if non-blocking connect finished ... */
                 lock_sock(sk);
-                if ((sk->sk_state == SMC_INIT) && (mask & EPOLLOUT)) {
-                        sk->sk_err = smc->clcsock->sk->sk_err;
-                        if (sk->sk_err) {
-                                mask |= EPOLLERR;
-                        } else {
+                sk->sk_err = smc->clcsock->sk->sk_err;
+                if (sk->sk_err) {
+                        mask |= EPOLLERR;
+                } else {
+                        /* if non-blocking connect finished ... */
+                        if (sk->sk_state == SMC_INIT &&
+                            mask & EPOLLOUT &&
+                            smc->clcsock->sk->sk_state != TCP_CLOSE) {
                                 rc = smc_connect_rdma(smc);
                                 if (rc < 0)
                                         mask |= EPOLLERR;