net: ipv4: devinet: Fix crash when add/del multicast IP with autojoin

When CONFIG_IP_MULTICAST is not set and multicast ip is added to the device
with autojoin flag or when multicast ip is deleted kernel will crash.

steps to reproduce:

ip addr add 224.0.0.0/32 dev eth0
ip addr del 224.0.0.0/32 dev eth0

or

ip addr add 224.0.0.0/32 dev eth0 autojoin

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000088
pc : _raw_write_lock_irqsave+0x1e0/0x2ac
lr : lock_sock_nested+0x1c/0x60
Call trace:
_raw_write_lock_irqsave+0x1e0/0x2ac
lock_sock_nested+0x1c/0x60
ip_mc_config.isra.28+0x50/0xe0
inet_rtm_deladdr+0x1a8/0x1f0
rtnetlink_rcv_msg+0x120/0x350
netlink_rcv_skb+0x58/0x120
rtnetlink_rcv+0x14/0x20
netlink_unicast+0x1b8/0x270
netlink_sendmsg+0x1a0/0x3b0
____sys_sendmsg+0x248/0x290
___sys_sendmsg+0x80/0xc0
__sys_sendmsg+0x68/0xc0
__arm64_sys_sendmsg+0x20/0x30
el0_svc_common.constprop.2+0x88/0x150
do_el0_svc+0x20/0x80
el0_sync_handler+0x118/0x190
el0_sync+0x140/0x180

Fixes: 93a714d6b53d ("multicast: Extend ip address command to enable multicast group join/leave on")
Signed-off-by: Taras Chornyi <[e-mail]>
Signed-off-by: Vadym Kochan <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/devinet.c

···
 	return NULL;
 }
 
-static int ip_mc_config(struct sock *sk, bool join, const struct in_ifaddr *ifa)
+static int ip_mc_autojoin_config(struct net *net, bool join,
+				 const struct in_ifaddr *ifa)
 {
+#if defined(CONFIG_IP_MULTICAST)
 	struct ip_mreqn mreq = {
 		.imr_multiaddr.s_addr = ifa->ifa_address,
 		.imr_ifindex = ifa->ifa_dev->dev->ifindex,
 	};
+	struct sock *sk = net->ipv4.mc_autojoin_sk;
 	int ret;
 
 	ASSERT_RTNL();
···
 	release_sock(sk);
 
 	return ret;
+#else
+	return -EOPNOTSUPP;
+#endif
 }
 
 static int inet_rtm_deladdr(struct sk_buff *skb, struct nlmsghdr *nlh,
···
 			continue;
 
 		if (ipv4_is_multicast(ifa->ifa_address))
-			ip_mc_config(net->ipv4.mc_autojoin_sk, false, ifa);
+			ip_mc_autojoin_config(net, false, ifa);
 		__inet_del_ifa(in_dev, ifap, 1, nlh, NETLINK_CB(skb).portid);
 		return 0;
 	}
···
 		 */
 		set_ifa_lifetime(ifa, valid_lft, prefered_lft);
 		if (ifa->ifa_flags & IFA_F_MCAUTOJOIN) {
-			int ret = ip_mc_config(net->ipv4.mc_autojoin_sk,
-					       true, ifa);
+			int ret = ip_mc_autojoin_config(net, true, ifa);
 
 			if (ret < 0) {
 				inet_free_ifa(ifa);