userns: xt_owner: Add basic user namespace support.

- Only allow adding matches from the initial user namespace
- Add the appropriate conversion functions to handle matches
against sockets in other user namespaces.

Cc: Jan Engelhardt <[e-mail]>
Cc: Patrick McHardy <[e-mail]>
Cc: Pablo Neira Ayuso <[e-mail]>
Acked-by: David S. Miller <[e-mail]>
Acked-by: Serge Hallyn <[e-mail]>
Signed-off-by: Eric W. Biederman <[e-mail]>

init/Kconfig

···
 
 	# Networking
 	depends on NET_9P = n
-	depends on NETFILTER_XT_MATCH_OWNER = n
 	depends on AF_RXRPC = n
 	depends on NET_KEY = n
 	depends on DNS_RESOLVER = n

net/netfilter/xt_owner.c

···
 #include <linux/netfilter/x_tables.h>
 #include <linux/netfilter/xt_owner.h>
 
+static int owner_check(const struct xt_mtchk_param *par)
+{
+	struct xt_owner_match_info *info = par->matchinfo;
+
+	/* For now only allow adding matches from the initial user namespace */
+	if ((info->match & (XT_OWNER_UID|XT_OWNER_GID)) &&
+	    (current_user_ns() != &init_user_ns))
+		return -EINVAL;
+	return 0;
+}
+
 static bool
 owner_mt(const struct sk_buff *skb, struct xt_action_param *par)
 {
···
 		return ((info->match ^ info->invert) &
 		       (XT_OWNER_UID | XT_OWNER_GID)) == 0;
 
-	if (info->match & XT_OWNER_UID)
-		if ((filp->f_cred->fsuid >= info->uid_min &&
-		    filp->f_cred->fsuid <= info->uid_max) ^
+	if (info->match & XT_OWNER_UID) {
+		kuid_t uid_min = make_kuid(&init_user_ns, info->uid_min);
+		kuid_t uid_max = make_kuid(&init_user_ns, info->uid_max);
+		if ((uid_gte(filp->f_cred->fsuid, uid_min) &&
+		     uid_lte(filp->f_cred->fsuid, uid_max)) ^
 		    !(info->invert & XT_OWNER_UID))
 			return false;
+	}
 
-	if (info->match & XT_OWNER_GID)
-		if ((filp->f_cred->fsgid >= info->gid_min &&
-		    filp->f_cred->fsgid <= info->gid_max) ^
+	if (info->match & XT_OWNER_GID) {
+		kgid_t gid_min = make_kgid(&init_user_ns, info->gid_min);
+		kgid_t gid_max = make_kgid(&init_user_ns, info->gid_max);
+		if ((gid_gte(filp->f_cred->fsgid, gid_min) &&
+		     gid_lte(filp->f_cred->fsgid, gid_max)) ^
 		    !(info->invert & XT_OWNER_GID))
 			return false;
+	}
 
 	return true;
 }
···
 	.name       = "owner",
 	.revision   = 1,
 	.family     = NFPROTO_UNSPEC,
+	.checkentry = owner_check,
 	.match      = owner_mt,
 	.matchsize  = sizeof(struct xt_owner_match_info),
 	.hooks      = (1 << NF_INET_LOCAL_OUT) |