[PATCH] j1939: fix unable to send messages with data length zero

[Alexander Hölzl]

The J1939 standard requires the transmission of messages of length 0.
For example the proprietary messages are specified with a data length
of 0 to 1785. The transmission of such messages was not possible.
Sending such a message resulted in no error being returned but no
corresponding can frame being generated.

Signed-off-by: Alexander Hölzl <alexander.hoelzl@xxxxxxx>
---
 net/can/j1939/socket.c    | 4 ++--
 net/can/j1939/transport.c | 5 +++--
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/can/j1939/socket.c b/net/can/j1939/socket.c
index 305dd72c844c..17226b2341d0 100644
--- a/net/can/j1939/socket.c
+++ b/net/can/j1939/socket.c
@@ -1132,7 +1132,7 @@ 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,
@@ -1177,7 +1177,7 @@ 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 319f47df3330..99832e60c08d 100644
--- a/net/can/j1939/transport.c
+++ b/net/can/j1939/transport.c
@@ -382,8 +382,9 @@ 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;
 		}
 	}
--
2.43.0