nfnetlink: do not ack malformed messages

Commit 0628b123c96d ("netfilter: nfnetlink: add batch support and use it
from nf_tables") introduced a bug leading to various crashes in netlink_ack
when netlink message with invalid nlmsg_len was sent by an unprivileged
user.

Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 3 deletions

diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index 027f16af51a0..046aa13b4fea 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -363,13 +363,15 @@ static void nfnetlink_rcv(struct sk_buff *skb)
         struct net *net = sock_net(skb->sk);
         int msglen;
 
-        if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
-                return netlink_ack(skb, nlh, -EPERM);
-
         if (nlh->nlmsg_len < NLMSG_HDRLEN ||
             skb->len < nlh->nlmsg_len)
                 return;
 
+        if (!ns_capable(net->user_ns, CAP_NET_ADMIN)) {
+                netlink_ack(skb, nlh, -EPERM);
+                return;
+        }
+
         if (nlh->nlmsg_type == NFNL_MSG_BATCH_BEGIN) {
                 struct nfgenmsg *nfgenmsg;