[PATCH] ipv4: Fix non-initialized TTL when CONFIG_SYSCTL=n

[PATCH] ipv4: Fix non-initialized TTL when CONFIG_SYSCTL=n

[Ezequiel Garcia]

Commit fa50d974d104 ("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: fa50d974d104 ("ipv4: Namespaceify ip_default_ttl sysctl knob")
Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
---
 net/ipv4/af_inet.c         | 8 ++++++++
 net/ipv4/sysctl_net_ipv4.c | 4 ----
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 2e6e65fc4d20..8d334816f89d 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1697,6 +1697,14 @@ 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;
 }
 
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index bb0419582b8d..1cb67de106fe 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/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:
-- 
2.7.0

Re: [PATCH] ipv4: Fix non-initialized TTL when CONFIG_SYSCTL=n

[David Miller]

From: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Date: Fri, 20 May 2016 13:21:10 -0300

> Commit fa50d974d104 ("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: fa50d974d104 ("ipv4: Namespaceify ip_default_ttl sysctl knob")
> Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>

Applied and queued up for -stable, thanks.