[SRU][T][X][A][B][PATCH 1/1] netfilter: xt_osf: Add missing permission checks

[Kleber Sacilotto de Souza]

From: Kevin Cernekee <cernekee at chromium.org>

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 at chromium.org>
Signed-off-by: Pablo Neira Ayuso <pablo at netfilter.org>

CVE-2017-17450
(cherry picked from commit 916a27901de01446bcf57ecca4783f6cff493309)
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
---
 net/netfilter/xt_osf.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/net/netfilter/xt_osf.c b/net/netfilter/xt_osf.c
index 647d989a01e6..de49ff18963a 100644
--- a/net/netfilter/xt_osf.c
+++ b/net/netfilter/xt_osf.c
@@ -20,6 +20,7 @@
 #include <linux/module.h>
 #include <linux/kernel.h>
 
+#include <linux/capability.h>
 #include <linux/if.h>
 #include <linux/inetdevice.h>
 #include <linux/ip.h>
@@ -70,6 +71,9 @@ static int xt_osf_add_callback(struct sock *ctnl, struct sk_buff *skb,
 	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;
 
@@ -113,6 +117,9 @@ static int xt_osf_remove_callback(struct sock *ctnl, struct sk_buff *skb,
 	struct xt_osf_finger *sf;
 	int err = -ENOENT;
 
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
 	if (!osf_attrs[OSF_ATTR_FINGER])
 		return -EINVAL;
 
-- 
2.14.1