ip: Fix data-races around sysctl_ip_default_ttl.

commit 8281b7ec5c upstream.

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

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/net/ethernet/netronome/nfp/flower/action.c

@@ -472,7 +472,7 @@ nfp_fl_set_tun(struct nfp_app *app, struct nfp_fl_set_tun *set_tun,
 			set_tun->ttl = ip4_dst_hoplimit(&rt->dst);
 			ip_rt_put(rt);
 		} else {
-			set_tun->ttl = net->ipv4.sysctl_ip_default_ttl;
+			set_tun->ttl = READ_ONCE(net->ipv4.sysctl_ip_default_ttl);
 		}
 	}
 

include/net/route.h

@@ -360,7 +360,7 @@ static inline int ip4_dst_hoplimit(const struct dst_entry *dst)
 	struct net *net = dev_net(dst->dev);
 
 	if (hoplimit == 0)
-		hoplimit = net->ipv4.sysctl_ip_default_ttl;
+		hoplimit = READ_ONCE(net->ipv4.sysctl_ip_default_ttl);
 	return hoplimit;
 }
 

net/ipv4/ip_sockglue.c

@@ -1597,7 +1597,7 @@ static int do_ip_getsockopt(struct sock *sk, int level, int optname,
 	{
 		struct net *net = sock_net(sk);
 		val = (inet->uc_ttl == -1 ?
-		       net->ipv4.sysctl_ip_default_ttl :
+		       READ_ONCE(net->ipv4.sysctl_ip_default_ttl) :
 		       inet->uc_ttl);
 		break;
 	}

net/ipv4/netfilter/nf_reject_ipv4.c

@@ -62,7 +62,7 @@ struct sk_buff *nf_reject_skb_v4_tcp_reset(struct net *net,
 
 	skb_reserve(nskb, LL_MAX_HEADER);
 	niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
-				   net->ipv4.sysctl_ip_default_ttl);
+				   READ_ONCE(net->ipv4.sysctl_ip_default_ttl));
 	nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
 	niph->tot_len = htons(nskb->len);
 	ip_send_check(niph);
@@ -115,7 +115,7 @@ struct sk_buff *nf_reject_skb_v4_unreach(struct net *net,
 
 	skb_reserve(nskb, LL_MAX_HEADER);
 	niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_ICMP,
-				   net->ipv4.sysctl_ip_default_ttl);
+				   READ_ONCE(net->ipv4.sysctl_ip_default_ttl));
 
 	skb_reset_transport_header(nskb);
 	icmph = skb_put_zero(nskb, sizeof(struct icmphdr));

net/ipv4/proc.c

@@ -387,7 +387,7 @@ static int snmp_seq_show_ipstats(struct seq_file *seq, void *v)
 
 	seq_printf(seq, "\nIp: %d %d",
 		   IPV4_DEVCONF_ALL(net, FORWARDING) ? 1 : 2,
-		   net->ipv4.sysctl_ip_default_ttl);
+		   READ_ONCE(net->ipv4.sysctl_ip_default_ttl));
 
 	BUILD_BUG_ON(offsetof(struct ipstats_mib, mibs) != 0);
 	snmp_get_cpu_field64_batch(buff64, snmp4_ipstats_list,

net/netfilter/nf_synproxy_core.c

@@ -427,7 +427,7 @@ synproxy_build_ip(struct net *net, struct sk_buff *skb, __be32 saddr,
 	iph->tos	= 0;
 	iph->id		= 0;
 	iph->frag_off	= htons(IP_DF);
-	iph->ttl	= net->ipv4.sysctl_ip_default_ttl;
+	iph->ttl	= READ_ONCE(net->ipv4.sysctl_ip_default_ttl);
 	iph->protocol	= IPPROTO_TCP;
 	iph->check	= 0;
 	iph->saddr	= saddr;