[PATCH 2/3] can: isotp: fix msg_namelen values depending on CAN_REQUIRED_SIZE

[Oliver Hartkopp <socketcan@hartkopp.net>]

Since commit f5223e9eee65 ("can: extend sockaddr_can to include j1939
members") the sockaddr_can has been extended in size and a new
CAN_REQUIRED_SIZE macro has been introduced to calculate the protocol
specific needed size.

The ABI for the msg_name and msg_namelen has not been adapted to the
new CAN_REQUIRED_SIZE macro for the other CAN protocols which leads
to a problem when an existing binary reads the (increased)
struct sockaddr_can in msg_name.

Fixes: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol")
Link: https://lore.kernel.org/linux-can/1135648123.112255.1616613706554.JavaMail.zimbra@nod.at/T/#t
Reported-by: Richard Weinberger <richard@nod.at>
Acked-by: Kurt Van Dijck <dev.kurt@vandijck-laurijssen.be>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 net/can/isotp.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/net/can/isotp.c b/net/can/isotp.c
index 15ea1234d457..9f94ad3caee9 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -75,10 +75,12 @@
 MODULE_DESCRIPTION("PF_CAN isotp 15765-2:2016 protocol");
 MODULE_LICENSE("Dual BSD/GPL");
 MODULE_AUTHOR("Oliver Hartkopp <socketcan@hartkopp.net>");
 MODULE_ALIAS("can-proto-6");
 
+#define ISOTP_MIN_NAMELEN CAN_REQUIRED_SIZE(struct sockaddr_can, can_addr.tp)
+
 #define SINGLE_MASK(id) (((id) & CAN_EFF_FLAG) ? \
 			 (CAN_EFF_MASK | CAN_EFF_FLAG | CAN_RTR_FLAG) : \
 			 (CAN_SFF_MASK | CAN_EFF_FLAG | CAN_RTR_FLAG))
 
 /* ISO 15765-2:2016 supports more than 4095 byte per ISO PDU as the FF_DL can
@@ -984,11 +986,12 @@ static int isotp_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
 	}
 
 	sock_recv_timestamp(msg, sk, skb);
 
 	if (msg->msg_name) {
-		msg->msg_namelen = sizeof(struct sockaddr_can);
+		__sockaddr_check_size(ISOTP_MIN_NAMELEN);
+		msg->msg_namelen = ISOTP_MIN_NAMELEN;
 		memcpy(msg->msg_name, skb->cb, msg->msg_namelen);
 	}
 
 	skb_free_datagram(sk, skb);
 
@@ -1054,11 +1057,11 @@ static int isotp_bind(struct socket *sock, struct sockaddr *uaddr, int len)
 	struct net_device *dev;
 	int err = 0;
 	int notify_enetdown = 0;
 	int do_rx_reg = 1;
 
-	if (len < CAN_REQUIRED_SIZE(struct sockaddr_can, can_addr.tp))
+	if (len < ISOTP_MIN_NAMELEN)
 		return -EINVAL;
 
 	/* do not register frame reception for functional addressing */
 	if (so->opt.flags & CAN_ISOTP_SF_BROADCAST)
 		do_rx_reg = 0;
@@ -1150,17 +1153,17 @@ static int isotp_getname(struct socket *sock, struct sockaddr *uaddr, int peer)
 	struct isotp_sock *so = isotp_sk(sk);
 
 	if (peer)
 		return -EOPNOTSUPP;
 
-	memset(addr, 0, sizeof(*addr));
+	memset(addr, 0, ISOTP_MIN_NAMELEN);
 	addr->can_family = AF_CAN;
 	addr->can_ifindex = so->ifindex;
 	addr->can_addr.tp.rx_id = so->rxid;
 	addr->can_addr.tp.tx_id = so->txid;
 
-	return sizeof(*addr);
+	return ISOTP_MIN_NAMELEN;
 }
 
 static int isotp_setsockopt(struct socket *sock, int level, int optname,
 			    sockptr_t optval, unsigned int optlen)
 {
-- 
2.30.2