isotp: isotp_sendmsg(): fix TX buffer concurrent access in isotp_send…

…msg()

When isotp_sendmsg() concurrent, tx.state of all TX processes can be
ISOTP_IDLE. The conditions so->tx.state != ISOTP_IDLE and
wq_has_sleeper(&so->wait) can not protect TX buffer from being
accessed by multiple TX processes.

We can use cmpxchg() to try to modify tx.state to ISOTP_SENDING firstly.
If the modification of the previous process succeed, the later process
must wait tx.state to ISOTP_IDLE firstly. Thus, we can ensure TX buffer
is accessed by only one process at the same time. And we should also
restore the original tx.state at the subsequent error processes.

Upstream commit 43a08c3bdac4

Fixes: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol")
Link: https://lore.kernel.org/all/c2517874fbdf4188585cf9ddf67a8fa74d5dbde5.1633764159.git.william.xuanziyang@huawei.com
Cc: stable@vger.kernel.org
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>

net/can/isotp.c

@@ -145,7 +145,7 @@ enum {
 struct tpcon {
 	int idx;
 	int len;
-	u8 state;
+	u32 state;
 	u8 bs;
 	u8 sn;
 	u8 ll_dl;
@@ -875,6 +875,7 @@ static int isotp_sendmsg(struct kiocb *iocb, struct socket *sock,
 {
 	struct sock *sk = sock->sk;
 	struct isotp_sock *so = isotp_sk(sk);
+	u32 old_state = so->tx.state;
 	struct sk_buff *skb;
 	struct net_device *dev;
 	struct canfd_frame *cf;
@@ -887,49 +888,57 @@ static int isotp_sendmsg(struct kiocb *iocb, struct socket *sock,
 		return -EADDRNOTAVAIL;
 
 	/* we do not support multiple buffers - for now */
-	if (so->tx.state != ISOTP_IDLE) {
-		if (msg->msg_flags & MSG_DONTWAIT)
-			return -EAGAIN;
+	if (cmpxchg(&so->tx.state, ISOTP_IDLE, ISOTP_SENDING) != ISOTP_IDLE ||
+	    wq_has_sleeper(&so->wait)) {
+		if (msg->msg_flags & MSG_DONTWAIT) {
+			err = -EAGAIN;
+			goto err_out;
+		}
 
 		/* wait for complete transmission of current pdu */
 		err = wait_event_interruptible(so->wait, so->tx.state == ISOTP_IDLE);
 		if (err)
-			return err;
+			goto err_out;
 	}
 
-	if (!size || size > MAX_MSG_LENGTH)
-		return -EINVAL;
+	if (!size || size > MAX_MSG_LENGTH) {
+		err = -EINVAL;
+		goto err_out;
+	}
 
 	/* take care of a potential SF_DL ESC offset for TX_DL > 8 */
 	off = (so->tx.ll_dl > CAN_MAX_DLEN) ? 1 : 0;
 
 	/* does the given data fit into a single frame for SF_BROADCAST? */
 	if ((so->opt.flags & CAN_ISOTP_SF_BROADCAST) &&
-	    (size > so->tx.ll_dl - SF_PCI_SZ4 - ae - off))
-		return -EINVAL;
+	    (size > so->tx.ll_dl - SF_PCI_SZ4 - ae - off)) {
+		err = -EINVAL;
+		goto err_out;
+	}
 
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(3,19,0)
 	err = memcpy_from_msg(so->tx.buf, msg, size);
 #else
 	err = memcpy_fromiovec(so->tx.buf, msg->msg_iov, size);
 #endif
 	if (err < 0)
-		return err;
+		goto err_out;
 
 	dev = dev_get_by_index(sock_net(sk), so->ifindex);
-	if (!dev)
-		return -ENXIO;
+	if (!dev) {
+		err = -ENXIO;
+		goto err_out;
+	}
 
 	skb = sock_alloc_send_skb(sk, so->ll.mtu + CAN_SKBRES,
 				  msg->msg_flags & MSG_DONTWAIT, &err);
 	if (!skb) {
 		dev_put(dev);
-		return err;
+		goto err_out;
 	}
 
 	isotp_skb_reserve(skb, dev);
 
-	so->tx.state = ISOTP_SENDING;
 	so->tx.len = size;
 	so->tx.idx = 0;
 
@@ -987,7 +996,7 @@ static int isotp_sendmsg(struct kiocb *iocb, struct socket *sock,
 	if (err) {
 		printk_once(KERN_NOTICE "can-isotp: %s: can_send_ret %d\n",
 			    __func__, err);
-		return err;
+		goto err_out;
 	}
 
 	if (wait_tx_done) {
@@ -996,6 +1005,13 @@ static int isotp_sendmsg(struct kiocb *iocb, struct socket *sock,
 	}
 
 	return size;
+
+err_out:
+	so->tx.state = old_state;
+	if (so->tx.state == ISOTP_IDLE)
+		wake_up_interruptible(&so->wait);
+
+	return err;
 }
 
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(4,1,0)