igmp: Fix regression caused by igmp sysctl namespace code.

Commit dcd87999d415 ("igmp: net: Move igmp namespace init to correct file")
moved the igmp sysctls initialization from tcp_sk_init to igmp_net_init. This
function is only called as part of per-namespace initialization, only if
CONFIG_IP_MULTICAST is defined, otherwise igmp_mc_init() call in ip_init is
compiled out, casuing the igmp pernet ops to not be registerd and those sysctl
being left initialized with 0. However, there are certain functions, such as
ip_mc_join_group which are always compiled and make use of some of those
sysctls. Let's do a partial revert of the aforementioned commit and move the
sysctl initialization back into tcp_sk_init, that way they will always have
sane values.

Fixes: dcd87999d415 ("igmp: net: Move igmp namespace init to correct file")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=196595
Reported-by: Gerardo Exequiel Pozzi <vmlinuz386@gmail.com>
Tested-by: Gerardo Exequiel Pozzi <vmlinuz386@gmail.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Cc: <stable@vger.kernel.org> # 4.6
---
 net/ipv4/igmp.c     | 6 ------
 net/ipv4/tcp_ipv4.c | 6 ++++++
 2 files changed, 6 insertions(+), 6 deletions(-)

On Wed, 2017-08-09 at 08:52 +0300, Nikolay Borisov wrote:
> Commit dcd87999d415 ("igmp: net: Move igmp namespace init to correct file")
> moved the igmp sysctls initialization from tcp_sk_init to igmp_net_init. This
> function is only called as part of per-namespace initialization, only if
> CONFIG_IP_MULTICAST is defined, otherwise igmp_mc_init() call in ip_init is
> compiled out, casuing the igmp pernet ops to not be registerd and those sysctl
> being left initialized with 0. However, there are certain functions, such as
> ip_mc_join_group which are always compiled and make use of some of those
> sysctls. Let's do a partial revert of the aforementioned commit and move the
> sysctl initialization back into tcp_sk_init, that way they will always have
> sane values.
> 
> Fixes: dcd87999d415 ("igmp: net: Move igmp namespace init to correct file")
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=196595
> Reported-by: Gerardo Exequiel Pozzi <vmlinuz386@gmail.com>
> Tested-by: Gerardo Exequiel Pozzi <vmlinuz386@gmail.com>
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> Cc: <stable@vger.kernel.org> # 4.6
> ---
>  net/ipv4/igmp.c     | 6 ------
>  net/ipv4/tcp_ipv4.c | 6 ++++++
>  2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
> index 28f14afd0dd3..498706b072fb 100644
> --- a/net/ipv4/igmp.c
> +++ b/net/ipv4/igmp.c
> @@ -2974,12 +2974,6 @@ static int __net_init igmp_net_init(struct net *net)
>  		goto out_sock;
>  	}
>  
> -	/* Sysctl initialization */
> -	net->ipv4.sysctl_igmp_max_memberships = 20;
> -	net->ipv4.sysctl_igmp_max_msf = 10;
> -	/* IGMP reports for link-local multicast groups are enabled by default */
> -	net->ipv4.sysctl_igmp_llm_reports = 1;
> -	net->ipv4.sysctl_igmp_qrv = 2;
>  	return 0;
>  
>  out_sock:
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index a20e7f03d5f7..64ba2c93d396 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -2528,6 +2528,12 @@ static int __net_init tcp_sk_init(struct net *net)
>  	net->ipv4.sysctl_tcp_window_scaling = 1;
>  	net->ipv4.sysctl_tcp_timestamps = 1;
>  
> +	net->ipv4.sysctl_igmp_max_memberships = 20;
> +	net->ipv4.sysctl_igmp_max_msf = 10;
> +	/* IGMP reports for link-local multicast groups are enabled by default */
> +	net->ipv4.sysctl_igmp_llm_reports = 1;
> +	net->ipv4.sysctl_igmp_qrv = 2;
> +
>  

I would rather move this to inet_init_net(), since IGMP does not belong
to TCP.

Thanks !