mptcp: prefer strscpy over strcpy

strcpy() performs no bounds checking on the destination buffer. This
could result in linear overflows beyond the end of the buffer, leading
to all kinds of misbehaviors. The safe replacement is strscpy() [1].

This is in preparation of a possible future step where all strcpy() uses
will be removed in favour of strscpy() [2].

This fixes CheckPatch warnings:

  WARNING: Prefer strscpy over strcpy

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strcpy [1]
Link: https://github.com/KSPP/linux/issues/88 [2]
Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20240514011335.176158-6-martineau@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/mptcp/ctrl.c

@@ -92,7 +92,7 @@ static void mptcp_pernet_set_defaults(struct mptcp_pernet *pernet)
 	pernet->allow_join_initial_addr_port = 1;
 	pernet->stale_loss_cnt = 4;
 	pernet->pm_type = MPTCP_PM_TYPE_KERNEL;
-	strcpy(pernet->scheduler, "default");
+	strscpy(pernet->scheduler, "default", sizeof(pernet->scheduler));
 }
 
 #ifdef CONFIG_SYSCTL

net/mptcp/protocol.c

@@ -2814,7 +2814,8 @@ static void mptcp_ca_reset(struct sock *sk)
 	struct inet_connection_sock *icsk = inet_csk(sk);
 
 	tcp_assign_congestion_control(sk);
-	strcpy(mptcp_sk(sk)->ca_name, icsk->icsk_ca_ops->name);
+	strscpy(mptcp_sk(sk)->ca_name, icsk->icsk_ca_ops->name,
+		sizeof(mptcp_sk(sk)->ca_name));
 
 	/* no need to keep a reference to the ops, the name will suffice */
 	tcp_cleanup_congestion_control(sk);
@@ -4169,7 +4170,7 @@ int __init mptcp_proto_v6_init(void)
 	int err;
 
 	mptcp_v6_prot = mptcp_prot;
-	strcpy(mptcp_v6_prot.name, "MPTCPv6");
+	strscpy(mptcp_v6_prot.name, "MPTCPv6", sizeof(mptcp_v6_prot.name));
 	mptcp_v6_prot.slab = NULL;
 	mptcp_v6_prot.obj_size = sizeof(struct mptcp6_sock);
 	mptcp_v6_prot.ipv6_pinfo_offset = offsetof(struct mptcp6_sock, np);

net/mptcp/sockopt.c

@@ -616,7 +616,7 @@ static int mptcp_setsockopt_sol_tcp_congestion(struct mptcp_sock *msk, sockptr_t
 	}
 
 	if (ret == 0)
-		strcpy(msk->ca_name, name);
+		strscpy(msk->ca_name, name, sizeof(msk->ca_name));
 
 	release_sock(sk);
 	return ret;