[PATCH] netfilter: nfnetlink_cthelper: Add missing permission checks

[Kevin Cernekee]

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 <cerne...@chromium.org>
---
 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