From b6256a620067ccceb3e707b80beb2cda8ba514b9 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Alexander=20H=C3=B6lzl?= Date: Wed, 5 Feb 2025 18:46:51 +0100 Subject: [PATCH] can: j1939: j1939_sk_send_loop(): fix unable to send messages with data length zero MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Acked-by: Oleksij Rempel 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 Signed-off-by: Greg Kroah-Hartman --- 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 c216c60f572b..45ae7a235dbf 100644 --- 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 84d63fb29ca1..c433b49f8715 100644 --- 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; } }