net: Use netlink_ns_capable to verify the permisions of netlink messages

It is possible by passing a netlink socket to a more privileged
executable and then to fool that executable into writing to the socket
data that happens to be valid netlink message to do something that
privileged executable did not intend to do.

To keep this from happening replace bare capable and ns_capable calls
with netlink_capable, netlink_net_calls and netlink_ns_capable calls.
Which act the same as the previous calls except they verify that the
opener of the socket had the desired permissions as well.

Reported-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 9 deletions

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index d4ff41739b0f..64ad17d077ed 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1395,7 +1395,8 @@ static int do_set_master(struct net_device *dev, int ifindex)
         return 0;
 }
 
-static int do_setlink(struct net_device *dev, struct ifinfomsg *ifm,
+static int do_setlink(const struct sk_buff *skb,
+                      struct net_device *dev, struct ifinfomsg *ifm,
                       struct nlattr **tb, char *ifname, int modified)
 {
         const struct net_device_ops *ops = dev->netdev_ops;
@@ -1407,7 +1408,7 @@ static int do_setlink(struct net_device *dev, struct ifinfomsg *ifm,
                         err = PTR_ERR(net);
                         goto errout;
                 }
-                if (!ns_capable(net->user_ns, CAP_NET_ADMIN)) {
+                if (!netlink_ns_capable(skb, net->user_ns, CAP_NET_ADMIN)) {
                         err = -EPERM;
                         goto errout;
                 }
@@ -1661,7 +1662,7 @@ static int rtnl_setlink(struct sk_buff *skb, struct nlmsghdr *nlh)
         if (err < 0)
                 goto errout;
 
-        err = do_setlink(dev, ifm, tb, ifname, 0);
+        err = do_setlink(skb, dev, ifm, tb, ifname, 0);
 errout:
         return err;
 }
@@ -1778,7 +1779,8 @@ err:
 }
 EXPORT_SYMBOL(rtnl_create_link);
 
-static int rtnl_group_changelink(struct net *net, int group,
+static int rtnl_group_changelink(const struct sk_buff *skb,
+                struct net *net, int group,
                 struct ifinfomsg *ifm,
                 struct nlattr **tb)
 {
@@ -1787,7 +1789,7 @@ static int rtnl_group_changelink(struct net *net, int group,
 
         for_each_netdev(net, dev) {
                 if (dev->group == group) {
-                        err = do_setlink(dev, ifm, tb, NULL, 0);
+                        err = do_setlink(skb, dev, ifm, tb, NULL, 0);
                         if (err < 0)
                                 return err;
                 }
@@ -1929,12 +1931,12 @@ replay:
                                 modified = 1;
                         }
 
-                        return do_setlink(dev, ifm, tb, ifname, modified);
+                        return do_setlink(skb, dev, ifm, tb, ifname, modified);
                 }
 
                 if (!(nlh->nlmsg_flags & NLM_F_CREATE)) {
                         if (ifm->ifi_index == 0 && tb[IFLA_GROUP])
-                                return rtnl_group_changelink(net,
+                                return rtnl_group_changelink(skb, net,
                                                 nla_get_u32(tb[IFLA_GROUP]),
                                                 ifm, tb);
                         return -ENODEV;
@@ -2321,7 +2323,7 @@ static int rtnl_fdb_del(struct sk_buff *skb, struct nlmsghdr *nlh)
         int err = -EINVAL;
         __u8 *addr;
 
-        if (!capable(CAP_NET_ADMIN))
+        if (!netlink_capable(skb, CAP_NET_ADMIN))
                 return -EPERM;
 
         err = nlmsg_parse(nlh, sizeof(*ndm), tb, NDA_MAX, NULL);
@@ -2773,7 +2775,7 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
         sz_idx = type>>2;
         kind = type&3;
 
-        if (kind != 2 && !ns_capable(net->user_ns, CAP_NET_ADMIN))
+        if (kind != 2 && !netlink_net_capable(skb, CAP_NET_ADMIN))
                 return -EPERM;
 
         if (kind == 2 && nlh->nlmsg_flags&NLM_F_DUMP) {