From: Alexander Hölzl <alexander.hoelzl@xxxxxxx> 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@xxxxxxx> Acked-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> Link: https://patch.msgid.link/20250205174651.103238-1-alexander.hoelzl@xxxxxxx Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol") Cc: stable@xxxxxxxxxxxxxxx [mkl: commit message rephrased] Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/can/j1939/socket.c | 4 ++-- net/can/j1939/transport.c | 5 +++-- 2 files changed, 5 insertions(+), 4 deletions(-) --- a/net/can/j1939/socket.c +++ b/net/can/j1939/socket.c @@ -1055,7 +1055,7 @@ static int j1939_sk_send_loop(struct j19 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 j19 todo_size -= segment_size; session->total_queued_size += segment_size; - } + } while (todo_size); switch (ret) { case 0: /* OK */ --- a/net/can/j1939/transport.c +++ b/net/can/j1939/transport.c @@ -378,8 +378,9 @@ sk_buff *j1939_session_skb_get_by_offset 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; } } Patches currently in stable-queue which might be from alexander.hoelzl@xxxxxxx are queue-5.4/can-j1939-j1939_sk_send_loop-fix-unable-to-send-messages-with-data-length-zero.patch
