[PATCH 5.10 37/95] can: isotp: isotp_sendmsg(): fix return error on FC timeout on TX path

[Greg Kroah-Hartman]

From: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>

commit d674a8f123b4096d85955c7eaabec688f29724c9 upstream.

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.

Fixes: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol")
Link: https://github.com/hartkopp/can-isotp/issues/42
Link: https://github.com/hartkopp/can-isotp/pull/43
Link: https://lore.kernel.org/all/20210507091839.1366379-1-mkl@xxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Sottas Guillaume (LMB) <Guillaume.Sottas@xxxxxxxxxxxx>
Tested-by: Oliver Hartkopp <socketcan@xxxxxxxxxxxx>
Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/can/isotp.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -953,6 +953,9 @@ static int isotp_sendmsg(struct socket *
 	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;