can: j1939: j1939_sk_send_loop(): fix unable to send messages with data length zero

commit 44de577e61ed239db09f0da9d436866bef9b77dd upstream.

The J1939 standard requires the transmission of messages of length 0.

For example proprietary messages are specified with a data length of 0
to 1785. The transmission of such messages is not possible. Sending
results in no error being returned but no corresponding can frame
being generated.

Enable the transmission of zero length J1939 messages. In order to
facilitate this two changes are necessary:

1) If the transmission of a new message is requested from user space
the message is segmented in j1939_sk_send_loop(). Let the segmentation
take into account zero length messages, do not terminate immediately,
queue the corresponding skb.

2) j1939_session_skb_get_by_offset() selects the next skb to transmit
for a session. Take into account that there might be zero length skbs
in the queue.

Signed-off-by: Alexander Hölzl <alexander.hoelzl@gmx.net>
Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20250205174651.103238-1-alexander.hoelzl@gmx.net
Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Cc: stable@vger.kernel.org
[mkl: commit message rephrased]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/can/j1939/socket.c b/net/can/j1939/socket.c
index c216c60f572b58fc3cbfff1b5b3fbc6aba8aa8b4..45ae7a235dbff3b2bccd87e8fd7c2885bdc2cc19 100644 (file)
--- a/net/can/j1939/socket.c
+++ b/net/can/j1939/socket.c
@@ -1055,7 +1055,7 @@ static int j1939_sk_send_loop(struct j1939_priv *priv,  struct sock *sk,
 
        todo_size = size;
 
-       while (todo_size) {
+       do {
                struct j1939_sk_buff_cb *skcb;
 
                segment_size = min_t(size_t, J1939_MAX_TP_PACKET_SIZE,
@@ -1100,7 +1100,7 @@ static int j1939_sk_send_loop(struct j1939_priv *priv,  struct sock *sk,
 
                todo_size -= segment_size;
                session->total_queued_size += segment_size;
-       }
+       } while (todo_size);
 
        switch (ret) {
        case 0: /* OK */

diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c
index 84d63fb29ca1fcb499271883d522b170abcd5104..c433b49f8715cb269cf81202d86155cb65b1c882 100644 (file)
--- a/net/can/j1939/transport.c
+++ b/net/can/j1939/transport.c
@@ -378,8 +378,9 @@ sk_buff *j1939_session_skb_get_by_offset(struct j1939_session *session,
        skb_queue_walk(&session->skb_queue, do_skb) {
                do_skcb = j1939_skb_to_cb(do_skb);
 
-               if (offset_start >= do_skcb->offset &&
-                   offset_start < (do_skcb->offset + do_skb->len)) {
+               if ((offset_start >= do_skcb->offset &&
+                    offset_start < (do_skcb->offset + do_skb->len)) ||
+                    (offset_start == 0 && do_skcb->offset == 0 && do_skb->len == 0)) {
                        skb = do_skb;
                }
        }