netfilter: ebtables: enforce CAP_NET_ADMIN

normal users are currently allowed to set/modify ebtables rules.
Restrict it to processes with CAP_NET_ADMIN.

Note that this cannot be reproduced with unmodified ebtables binary
because it uses SOCK_RAW.
Signed-off-by: NFlorian Westphal <fwestphal@astaro.com>
Cc: stable@kernel.org
Signed-off-by: NPatrick McHardy <kaber@trash.net>

net/bridge/netfilter/ebtables.c

@@ -1406,6 +1406,9 @@ static int do_ebt_set_ctl(struct sock *sk,
 {
 	int ret;
 
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
 	switch(cmd) {
 	case EBT_SO_SET_ENTRIES:
 		ret = do_replace(sock_net(sk), user, len);
@@ -1425,6 +1428,9 @@ static int do_ebt_get_ctl(struct sock *sk, int cmd, void __user *user, int *len)
 	struct ebt_replace tmp;
 	struct ebt_table *t;
 
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
 	if (copy_from_user(&tmp, user, sizeof(tmp)))
 		return -EFAULT;