[PATCH v2] can: isotp: isotp_sendmsg(): fix return error on FC timeout on TX path

[Marc Kleine-Budde <mkl@pengutronix.de>]

When the a large chunk of data send and the receiver does not send a
Flow Control frame back in time, the sendmsg() does not return a error
code, but the number of bytes sent corresponding to the size of the
packet.

If a timeout occurs the isotp_tx_timer_handler() is fired, sets
sk->sk_err and calls the sk->sk_error_report() function. It was
wrongly expected that the error would be propagated to user space in
every case. For isotp_sendmsg() blocking on wait_event_interruptible()
this is not the case.

This patch fixes the problem by checking if sk->sk_err is set and
returning the error to user space.

Link: https://github.com/hartkopp/can-isotp/issues/42
Link: https://github.com/hartkopp/can-isotp/pull/43
Cc: Oliver Hartkopp <socketcan@hartkopp.net>
Cc: Sottas Guillaume (LMB) <Guillaume.Sottas@liebherr.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
Changes since v1:
- add proper patch descriptiom
- return negative error value

 net/can/isotp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/can/isotp.c b/net/can/isotp.c
index 9f94ad3caee9..d2601717211d 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -954,6 +954,9 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 	if (wait_tx_done) {
 		/* wait for complete transmission of current pdu */
 		wait_event_interruptible(so->wait, so->tx.state == ISOTP_IDLE);
+
+		if (sk->sk_err)
+			return -sk->sk_err;
 	}
 
 	return size;
-- 
2.30.2