net: Use ns_capable_noaudit() when determining net sysctl permissions

The capability check should not be audited since it is only being used
to determine the inode permissions. A failed check does not indicate a
violation of security policy but, when an LSM is enabled, a denial audit
message was being generated.

The denial audit message caused confusion for some application authors
because root-running Go applications always triggered the denial. To
prevent this confusion, the capability check in net_ctl_permissions() is
switched to the noaudit variant.

BugLink: https://launchpad.net/bugs/1465724

Signed-off-by: Tyler Hicks <[e-mail]>
Acked-by: Serge E. Hallyn <[e-mail]>
Signed-off-by: James Morris <[e-mail]>
[dtor: reapplied after e79c6a4fc923 ("net: make net namespace sysctls
belong to container's owner") accidentally reverted the change.]
Signed-off-by: Dmitry Torokhov <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/sysctl_net.c

···
 	struct net *net = container_of(head->set, struct net, sysctls);
 
 	/* Allow network administrator to have same access as root. */
-	if (ns_capable(net->user_ns, CAP_NET_ADMIN)) {
+	if (ns_capable_noaudit(net->user_ns, CAP_NET_ADMIN)) {
 		int mode = (table->mode >> 6) & 7;
 		return (mode << 6) | (mode << 3) | mode;
 	}