ipv4: Fix non-initialized TTL when CONFIG_SYSCTL=n

Commit fa50d974 ("ipv4: Namespaceify ip_default_ttl sysctl knob")
moves the default TTL assignment, and as side-effect IPv4 TTL now
has a default value only if sysctl support is enabled (CONFIG_SYSCTL=y).

The sysctl_ip_default_ttl is fundamental for IP to work properly,
as it provides the TTL to be used as default. The defautl TTL may be
used in ip_selected_ttl, through the following flow:

  ip_select_ttl
    ip4_dst_hoplimit
      net->ipv4.sysctl_ip_default_ttl

This commit fixes the issue by assigning net->ipv4.sysctl_ip_default_ttl
in net_init_net, called during ipv4's initialization.

Without this commit, a kernel built without sysctl support will send
all IP packets with zero TTL (unless a TTL is explicitly set, e.g.
with setsockopt).

Given a similar issue might appear on the other knobs that were
namespaceify, this commit also moves them.

Fixes: fa50d974 ("ipv4: Namespaceify ip_default_ttl sysctl knob")
Signed-off-by: NEzequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/af_inet.c

@@ -1681,6 +1681,14 @@ static __net_init int inet_init_net(struct net *net)
 	 */
 	net->ipv4.ping_group_range.range[0] = make_kgid(&init_user_ns, 1);
 	net->ipv4.ping_group_range.range[1] = make_kgid(&init_user_ns, 0);
+
+	/* Default values for sysctl-controlled parameters.
+	 * We set them here, in case sysctl is not compiled.
+	 */
+	net->ipv4.sysctl_ip_default_ttl = IPDEFTTL;
+	net->ipv4.sysctl_ip_dynaddr = 0;
+	net->ipv4.sysctl_ip_early_demux = 1;
+
 	return 0;
 }
 

net/ipv4/sysctl_net_ipv4.c

@@ -999,10 +999,6 @@ static __net_init int ipv4_sysctl_init_net(struct net *net)
 	if (!net->ipv4.sysctl_local_reserved_ports)
 		goto err_ports;
 
-	net->ipv4.sysctl_ip_default_ttl = IPDEFTTL;
-	net->ipv4.sysctl_ip_dynaddr = 0;
-	net->ipv4.sysctl_ip_early_demux = 1;
-
 	return 0;
 
 err_ports: