icmp: Fix a data-race around sysctl_icmp_ratemask.

While reading sysctl_icmp_ratemask, it can be changed concurrently.
Thus, we need to add READ_ONCE() to its reader.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/icmp.c

@@ -282,7 +282,7 @@ static bool icmpv4_mask_allow(struct net *net, int type, int code)
 		return true;
 
 	/* Limit if icmp type is enabled in ratemask. */
-	if (!((1 << type) & net->ipv4.sysctl_icmp_ratemask))
+	if (!((1 << type) & READ_ONCE(net->ipv4.sysctl_icmp_ratemask)))
 		return true;
 
 	return false;