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

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.

Signed-off-by: Jann Horn <redacted>
---
 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

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.

From: Pablo Neira Ayuso <pablo@netfilter.org>
Date: Thu, 20 Oct 2016 20:22:24 +0200

On Sat, Sep 24, 2016 at 12:21:04AM +0200, Jann Horn wrote:

quoted

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.

In the commit message for the -stable submission simply say "Not
applicable" in the upstream commit reference.  Like:

	[ Upstream commit: Not applicable ]

or something like that.

On Thu, Oct 20, 2016 at 02:37:47PM -0400, David Miller wrote:

From: Pablo Neira Ayuso <pablo@netfilter.org>
Date: Thu, 20 Oct 2016 20:22:24 +0200

quoted

On Sat, Sep 24, 2016 at 12:21:04AM +0200, Jann Horn wrote:

quoted

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.

In the commit message for the -stable submission simply say "Not
applicable" in the upstream commit reference.  Like:

	[ Upstream commit: Not applicable ]

or something like that.

Who should do that? Me, after getting a maintainer ack? Or the maintainer?

From: Jann Horn <redacted>
Date: Sat, 22 Oct 2016 23:23:42 +0200

On Thu, Oct 20, 2016 at 02:37:47PM -0400, David Miller wrote:

quoted

From: Pablo Neira Ayuso <pablo@netfilter.org>
Date: Thu, 20 Oct 2016 20:22:24 +0200

quoted

On Sat, Sep 24, 2016 at 12:21:04AM +0200, Jann Horn wrote:

quoted

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.

In the commit message for the -stable submission simply say "Not
applicable" in the upstream commit reference.  Like:

	[ Upstream commit: Not applicable ]

or something like that.

Who should do that? Me, after getting a maintainer ack? Or the maintainer?

When the maintainer submits a patch to -stable, that's what they
add to the commit message.