net: Fix ns_capable check in sock_diag_put_filterinfo

commit 78541c1d upstream.

The caller needs capabilities on the namespace being queried, not on
their own namespace.  This is a security bug, although it likely has
only a minor impact.
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

include/linux/sock_diag.h

@@ -23,7 +23,7 @@ int sock_diag_check_cookie(void *sk, __u32 *cookie);
 void sock_diag_save_cookie(void *sk, __u32 *cookie);
 
 int sock_diag_put_meminfo(struct sock *sk, struct sk_buff *skb, int attr);
-int sock_diag_put_filterinfo(struct user_namespace *user_ns, struct sock *sk,
+int sock_diag_put_filterinfo(struct sock *sk,
 			     struct sk_buff *skb, int attrtype);
 
 #endif

net/core/sock_diag.c

@@ -49,7 +49,7 @@ int sock_diag_put_meminfo(struct sock *sk, struct sk_buff *skb, int attrtype)
 }
 EXPORT_SYMBOL_GPL(sock_diag_put_meminfo);
 
-int sock_diag_put_filterinfo(struct user_namespace *user_ns, struct sock *sk,
+int sock_diag_put_filterinfo(struct sock *sk,
 			     struct sk_buff *skb, int attrtype)
 {
 	struct nlattr *attr;
@@ -57,7 +57,7 @@ int sock_diag_put_filterinfo(struct user_namespace *user_ns, struct sock *sk,
 	unsigned int len;
 	int err = 0;
 
-	if (!ns_capable(user_ns, CAP_NET_ADMIN)) {
+	if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)) {
 		nla_reserve(skb, attrtype, 0);
 		return 0;
 	}

net/packet/diag.c

@@ -171,7 +171,7 @@ static int sk_diag_fill(struct sock *sk, struct sk_buff *skb,
 		goto out_nlmsg_trim;
 
 	if ((req->pdiag_show & PACKET_SHOW_FILTER) &&
-	    sock_diag_put_filterinfo(user_ns, sk, skb, PACKET_DIAG_FILTER))
+	    sock_diag_put_filterinfo(sk, skb, PACKET_DIAG_FILTER))
 		goto out_nlmsg_trim;
 
 	return nlmsg_end(skb, nlh);