linux-kernel - [PATCH 4.4 40/74] netfilter: xt_osf: Add missing permission checks

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Message-Id: <20180129123849.389817535@linuxfoundation.org>
Date:   Mon, 29 Jan 2018 13:56:45 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Kevin Cernekee <cernekee@...omium.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Michal Kubecek <mkubecek@...e.cz>
Subject: [PATCH 4.4 40/74] netfilter: xt_osf: Add missing permission checks

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kevin Cernekee <cernekee@...omium.org>

commit 916a27901de01446bcf57ecca4783f6cff493309 upstream.

The capability check in nfnetlink_rcv() verifies that the caller
has CAP_NET_ADMIN in the namespace that "owns" the netlink socket.
However, xt_osf_fingers 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:

    vpnns -- nfnl_osf -f /tmp/pf.os

    vpnns -- nfnl_osf -f /tmp/pf.os -d

These non-root operations successfully modify the systemwide OS
fingerprint list.  Add new capable() checks so that they can't.

Signed-off-by: Kevin Cernekee <cernekee@...omium.org>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Acked-by: Michal Kubecek <mkubecek@...e.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/netfilter/xt_osf.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/net/netfilter/xt_osf.c
+++ b/net/netfilter/xt_osf.c
@@ -19,6 +19,7 @@
 #include <linux/module.h>
 #include <linux/kernel.h>
 
+#include <linux/capability.h>
 #include <linux/if.h>
 #include <linux/inetdevice.h>
 #include <linux/ip.h>
@@ -69,6 +70,9 @@ static int xt_osf_add_callback(struct so
 	struct xt_osf_finger *kf = NULL, *sf;
 	int err = 0;
 
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
 	if (!osf_attrs[OSF_ATTR_FINGER])
 		return -EINVAL;
 
@@ -112,6 +116,9 @@ static int xt_osf_remove_callback(struct
 	struct xt_osf_finger *sf;
 	int err = -ENOENT;
 
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
 	if (!osf_attrs[OSF_ATTR_FINGER])
 		return -EINVAL;