[PATCH can-next v2 1/3] af_can: ensure sk_protocol is always set on socket creation

[Filippo Storniolo <fstornio@redhat.com>]

From: Davide Caratti <dcaratti@redhat.com>

Currently, only j1939 assigns a value to 'sk_protocol'. As a prerequisite
for the implementation of CAN sockets diagnostics, AF_CAN sockets need an
easy way to determine which protocol is on top of an existing socket.

POC test using can-tests:

 | # perf probe -m can_j1939 --add "j1939_sk_recvmsg sock->sk->sk_protocol"
 | # perf record -e probe:j1939_sk_recvmsg -aR -- ./j1939/tst-j1939-ac
 | [...]
 | # perf script
 | tst-j1939-ac  5807 [002] 322767.312599: probe:j1939_sk_recvmsg: (ffffffffc0b29a14) sk_protocol=0x7
 |  ^^^ 0x7, that's CAN_J1939

 | # perf probe -m can_raw --add "raw_recvmsg sock->sk->sk_protocol"
 | # perf record -e probe:raw_recvmsg -aR ./netlayer/tst-rcv-own-msgs vcan0
 | # perf script
 | [...]
 | tst-rcv-own-msg  5816 [001] 323173.651122: probe:raw_recvmsg: (ffffffffc0b20154) sk_protocol=0x1
 |  ^^^ 0x1, that's CAN_RAW. It was 0x0 on unpatched kernel

Storing the "protocol" value in can_create() fixes the problem. This also
fixes AF_CAN support for the following system call:

 | getsockopt(..., SOL_SOCKET, SO_PROTOCOL, &proto, sizeof(proto))

that was assigning 0 to 'proto' since the earliest kernel versions.

Fixes: 0d66548a10cb ("[CAN]: Add PF_CAN core module")
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
---
 net/can/af_can.c       | 1 +
 net/can/j1939/socket.c | 1 -
 2 files changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/can/af_can.c b/net/can/af_can.c
index 7bc86b176b4d..65af25946985 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -162,6 +162,7 @@ static int can_create(struct net *net, struct socket *sock, int protocol,
 	}
 
 	sock_init_data(sock, sk);
+	sk->sk_protocol = protocol;
 	sk->sk_destruct = can_sock_destruct;
 
 	if (sk->sk_prot->init)
diff --git a/net/can/j1939/socket.c b/net/can/j1939/socket.c
index 50a598ef5fd4..ccd43ff5519c 100644
--- a/net/can/j1939/socket.c
+++ b/net/can/j1939/socket.c
@@ -420,7 +420,6 @@ static int j1939_sk_init(struct sock *sk)
 	/* j1939_sk_sock_destruct() depends on SOCK_RCU_FREE flag */
 	sock_set_flag(sk, SOCK_RCU_FREE);
 	sk->sk_destruct = j1939_sk_sock_destruct;
-	sk->sk_protocol = CAN_J1939;
 
 	return 0;
 }

-- 
2.55.0