Subject: Re: [PATCH] netfilter: don't permit unprivileged writes to global state via sysctls

From: Pablo Neira Ayuso <[email-masked]>
Date: Thu, 20 Oct 2016 20:22:24 +0200

On Sat, Sep 24, 2016 at 12:21:04AM +0200, Jann Horn wrote:
> This prevents the modification of nf_conntrack_max in unprivileged network
> namespaces. For unprivileged network namespaces, ip_conntrack_max is kept
> as a readonly sysctl in order to minimize potential compatibility issues.
> 
> This patch should apply cleanly to the net tree.

For the record: This patch looks good to me, but this legacy
ip_conntrack sysctl code is now gone.

I don't know what is the procedure to get this to -stable branches now
that this cannot be pushed upstream.

> Signed-off-by: Jann Horn <[email-masked]>
> ---
>  net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
> index ae1a71a..a639e94 100644
> --- a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
> +++ b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
> @@ -358,6 +358,9 @@ static int ipv4_init_net(struct net *net)
>  	if (!in->ctl_table)
>  		return -ENOMEM;
>  
> +	if (net->user_ns != &init_user_ns)
> +		in->ctl_table[0].mode = 0444;
> +
>  	in->ctl_table[0].data = &nf_conntrack_max;
>  	in->ctl_table[1].data = &net->ct.count;
>  	in->ctl_table[2].data = &nf_conntrack_htable_size;
> -- 
> 2.1.4
>