tls: wait for async encrypt in case of error during latter iterations of sendmsg

If we hit an error during the main loop of tls_sw_sendmsg_locked (eg
failed allocation), we jump to send_end and immediately
return. Previous iterations may have queued async encryption requests
that are still pending. We should wait for those before returning, as
we could otherwise be reading from memory that userspace believes
we're not using anymore, which would be a sort of use-after-free.

This is similar to what tls_sw_recvmsg already does: failures during
the main loop jump to the "wait for async" code, not straight to the
unlock/return.

Fixes: a42055e ("net/tls: Add support for async encryption of records for performance")
Reported-by: Jann Horn <[email protected]>
Signed-off-by: Sabrina Dubroca <[email protected]>
Link: https://patch.msgid.link/c793efe9673b87f808d84fdefc0f732217030c52.1760432043.git.sd@queasysnail.net
Signed-off-by: Jakub Kicinski <[email protected]>

Author: qsn

net/tls/tls_sw.c

@@ -1054,7 +1054,7 @@ static int tls_sw_sendmsg_locked(struct sock *sk, struct msghdr *msg,
 			if (ret == -EINPROGRESS)
 				num_async++;
 			else if (ret != -EAGAIN)
-				goto send_end;
+				goto end;
 		}
 	}
 
@@ -1226,8 +1226,9 @@ static int tls_sw_sendmsg_locked(struct sock *sk, struct msghdr *msg,
 			goto alloc_encrypted;
 	}
 
+send_end:
 	if (!num_async) {
-		goto send_end;
+		goto end;
 	} else if (num_zc || eor) {
 		int err;
 
@@ -1245,7 +1246,7 @@ static int tls_sw_sendmsg_locked(struct sock *sk, struct msghdr *msg,
 		tls_tx_records(sk, msg->msg_flags);
 	}
 
-send_end:
+end:
 	ret = sk_stream_error(sk, msg->msg_flags, ret);
 	return copied > 0 ? copied : ret;
 }