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Subject[PATCH] netfilter: xt_osf: 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, 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()

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 <>
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 36e14b1..a34f314 100644
--- 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>
@@ -70,6 +71,9 @@ static int xt_osf_add_callback(struct net *net, struct sock *ctnl,
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;

@@ -115,6 +119,9 @@ static int xt_osf_remove_callback(struct net *net, struct sock *ctnl,
struct xt_osf_finger *sf;
int err = -ENOENT;

+ if (!capable(CAP_NET_ADMIN))
+ return -EPERM;
if (!osf_attrs[OSF_ATTR_FINGER])
return -EINVAL;

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