af_unix: preserve const qualifier in unix_sk()

We can change unix_sk() to propagate its argument const qualifier,
thanks to container_of_const().

We need to change dump_common_audit_data() 'struct unix_sock *u'
local var to get a const attribute.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/af_unix.h

@@ -74,10 +74,7 @@ struct unix_sock {
 #endif
 };
 
-static inline struct unix_sock *unix_sk(const struct sock *sk)
-{
-	return (struct unix_sock *)sk;
-}
+#define unix_sk(ptr) container_of_const(ptr, struct unix_sock, sk)
 
 #define peer_wait peer_wq.wait
 

security/lsm_audit.c

@@ -310,7 +310,7 @@ static void dump_common_audit_data(struct audit_buffer *ab,
 	case LSM_AUDIT_DATA_NET:
 		if (a->u.net->sk) {
 			const struct sock *sk = a->u.net->sk;
-			struct unix_sock *u;
+			const struct unix_sock *u;
 			struct unix_address *addr;
 			int len = 0;
 			char *p = NULL;