2017-12-03 20:12:52

by Kevin Cernekee

Subject: [PATCH] netfilter: nfnetlink_cthelper: Add missing permission checks

The capability check in nfnetlink_rcv() verifies that the caller
has CAP_NET_ADMIN in the namespace that "owns" the netlink socket.
However, nfnl_cthelper_list is shared by all net namespaces on the
system. An unprivileged user can create user and net namespaces
in which he holds CAP_NET_ADMIN to bypass the netlink_net_capable()
check:

$ nfct helper list
nfct v1.4.4: netlink error: Operation not permitted
$ vpnns -- nfct helper list
{
.name = ftp,
.queuenum = 0,
.l3protonum = 2,
.l4protonum = 6,
.priv_data_len = 24,
.status = enabled,
};

Add capable() checks in nfnetlink_cthelper, as this is cleaner than
trying to generalize the solution.

Signed-off-by: Kevin Cernekee <[email protected]>
---
net/netfilter/nfnetlink_cthelper.c | 10 ++++++++++
1 file changed, 10 insertions(+)


I think xt_osf has the same issue with respect to xt_osf_fingers.
Also, it looks like nlmon devices created in an unprivileged netns can
see netlink activity from the init namespace.


diff --git a/net/netfilter/nfnetlink_cthelper.c b/net/netfilter/nfnetlink_cthelper.c
index 41628b393673..d33ce6d5ebce 100644
--- a/net/netfilter/nfnetlink_cthelper.c
+++ b/net/netfilter/nfnetlink_cthelper.c
@@ -17,6 +17,7 @@
#include <linux/types.h>
#include <linux/list.h>
#include <linux/errno.h>
+#include <linux/capability.h>
#include <net/netlink.h>
#include <net/sock.h>

@@ -407,6 +408,9 @@ static int nfnl_cthelper_new(struct net *net, struct sock *nfnl,
struct nfnl_cthelper *nlcth;
int ret = 0;

+ if (!capable(CAP_NET_ADMIN))
+ return -EPERM;
+
if (!tb[NFCTH_NAME] || !tb[NFCTH_TUPLE])
return -EINVAL;

@@ -611,6 +615,9 @@ static int nfnl_cthelper_get(struct net *net, struct sock *nfnl,
struct nfnl_cthelper *nlcth;
bool tuple_set = false;

+ if (!capable(CAP_NET_ADMIN))
+ return -EPERM;
+
if (nlh->nlmsg_flags & NLM_F_DUMP) {
struct netlink_dump_control c = {
.dump = nfnl_cthelper_dump_table,
@@ -678,6 +685,9 @@ static int nfnl_cthelper_del(struct net *net, struct sock *nfnl,
struct nfnl_cthelper *nlcth, *n;
int j = 0, ret;

+ if (!capable(CAP_NET_ADMIN))
+ return -EPERM;
+
if (tb[NFCTH_NAME])
helper_name = nla_data(tb[NFCTH_NAME]);

--
2.7.4

2017-12-04 10:32:09

by Pablo Neira Ayuso

Subject: Re: [PATCH] netfilter: nfnetlink_cthelper: Add missing permission checks

On Sun, Dec 03, 2017 at 12:12:45PM -0800, Kevin Cernekee wrote:
> The capability check in nfnetlink_rcv() verifies that the caller
> has CAP_NET_ADMIN in the namespace that "owns" the netlink socket.
> However, nfnl_cthelper_list is shared by all net namespaces on the
> system.

Right, we need per-netns support for nfnetlink_cthelper.

> An unprivileged user can create user and net namespaces
> in which he holds CAP_NET_ADMIN to bypass the netlink_net_capable()
> check:

Applied to nf, thanks.
[...]
> I think xt_osf has the same issue with respect to xt_osf_fingers.
> Also, it looks like nlmon devices created in an unprivileged netns can
> see netlink activity from the init namespace.

A fix that one would be good too.