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

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Message-Id: <20211019071518.2346320-2-mkl@pengutronix.de>
Date:   Tue, 19 Oct 2021 09:15:18 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, linux-can@...r.kernel.org,
        kernel@...gutronix.de, Marc Kleine-Budde <mkl@...gutronix.de>,
        stable@...r.kernel.org,
        Sottas Guillaume <Guillaume.Sottas@...bherr.com>,
        Oliver Hartkopp <socketcan@...tkopp.net>
Subject: [PATCH net] can: isotp: isotp_sendmsg(): fix return error on FC timeout on TX path

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@pengutronix.de
Cc: stable@...r.kernel.org
Reported-by: Sottas Guillaume (LMB) <Guillaume.Sottas@...bherr.com>
Tested-by: Oliver Hartkopp <socketcan@...tkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
---
 net/can/isotp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/can/isotp.c b/net/can/isotp.c
index d1f54273c0bb..df6968b28bf4 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -971,6 +971,9 @@ 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;

base-commit: 8a64ef042eab8a6cec04a6c79d44d1af79b628ca
-- 
2.33.0