keys: Network namespace domain tag

Create key domain tags for network namespaces and make it possible to
automatically tag keys that are used by networked services (e.g. AF_RXRPC,
AFS, DNS) with the default network namespace if not set by the caller.

This allows keys with the same description but in different namespaces to
coexist within a keyring.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: netdev@vger.kernel.org
cc: linux-nfs@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: linux-afs@lists.infradead.org

include/linux/key-type.h

@@ -74,6 +74,9 @@ struct key_type {
 	 */
 	size_t def_datalen;
 
+	unsigned int flags;
+#define KEY_TYPE_NET_DOMAIN	0x00000001 /* Keys of this type have a net namespace domain */
+
 	/* vet a description */
 	int (*vet_description)(const char *description);
 

include/net/net_namespace.h

@@ -71,6 +71,9 @@ struct net {
 						 */
 	struct llist_node	cleanup_list;	/* namespaces on death row */
 
+#ifdef CONFIG_KEYS
+	struct key_tag		*key_domain;	/* Key domain of operation tag */
+#endif
 	struct user_namespace   *user_ns;	/* Owning user namespace */
 	struct ucounts		*ucounts;
 	spinlock_t		nsid_lock;

net/core/net_namespace.c

@@ -38,9 +38,16 @@ EXPORT_SYMBOL_GPL(net_namespace_list);
 DECLARE_RWSEM(net_rwsem);
 EXPORT_SYMBOL_GPL(net_rwsem);
 
+#ifdef CONFIG_KEYS
+static struct key_tag init_net_key_domain = { .usage = REFCOUNT_INIT(1) };
+#endif
+
 struct net init_net = {
 	.count		= REFCOUNT_INIT(1),
 	.dev_base_head	= LIST_HEAD_INIT(init_net.dev_base_head),
+#ifdef CONFIG_KEYS
+	.key_domain	= &init_net_key_domain,
+#endif
 };
 EXPORT_SYMBOL(init_net);
 
@@ -386,10 +393,22 @@ static struct net *net_alloc(void)
 	if (!net)
 		goto out_free;
 
+#ifdef CONFIG_KEYS
+	net->key_domain = kzalloc(sizeof(struct key_tag), GFP_KERNEL);
+	if (!net->key_domain)
+		goto out_free_2;
+	refcount_set(&net->key_domain->usage, 1);
+#endif
+
 	rcu_assign_pointer(net->gen, ng);
 out:
 	return net;
 
+#ifdef CONFIG_KEYS
+out_free_2:
+	kmem_cache_free(net_cachep, net);
+	net = NULL;
+#endif
 out_free:
 	kfree(ng);
 	goto out;
@@ -566,6 +585,7 @@ static void cleanup_net(struct work_struct *work)
 	list_for_each_entry_safe(net, tmp, &net_exit_list, exit_list) {
 		list_del_init(&net->exit_list);
 		dec_net_namespaces(net->ucounts);
+		key_remove_domain(net->key_domain);
 		put_user_ns(net->user_ns);
 		net_drop_ns(net);
 	}

net/dns_resolver/dns_key.c

@@ -314,6 +314,7 @@ static long dns_resolver_read(const struct key *key,
 
 struct key_type key_type_dns_resolver = {
 	.name		= "dns_resolver",
+	.flags		= KEY_TYPE_NET_DOMAIN,
 	.preparse	= dns_resolver_preparse,
 	.free_preparse	= dns_resolver_free_preparse,
 	.instantiate	= generic_key_instantiate,

net/rxrpc/key.c

@@ -43,6 +43,7 @@ static long rxrpc_read(const struct key *, char __user *, size_t);
  */
 struct key_type key_type_rxrpc = {
 	.name		= "rxrpc",
+	.flags		= KEY_TYPE_NET_DOMAIN,
 	.preparse	= rxrpc_preparse,
 	.free_preparse	= rxrpc_free_preparse,
 	.instantiate	= generic_key_instantiate,
@@ -58,6 +59,7 @@ EXPORT_SYMBOL(key_type_rxrpc);
  */
 struct key_type key_type_rxrpc_s = {
 	.name		= "rxrpc_s",
+	.flags		= KEY_TYPE_NET_DOMAIN,
 	.vet_description = rxrpc_vet_description_s,
 	.preparse	= rxrpc_preparse_s,
 	.free_preparse	= rxrpc_free_preparse_s,

security/keys/keyring.c

@@ -17,10 +17,12 @@
 #include <linux/seq_file.h>
 #include <linux/err.h>
 #include <linux/user_namespace.h>
+#include <linux/nsproxy.h>
 #include <keys/keyring-type.h>
 #include <keys/user-type.h>
 #include <linux/assoc_array_priv.h>
 #include <linux/uaccess.h>
+#include <net/net_namespace.h>
 #include "internal.h"
 
 /*
@@ -220,7 +222,10 @@ void key_set_index_key(struct keyring_index_key *index_key)
 
 	memcpy(index_key->desc, index_key->description, n);
 
-	index_key->domain_tag = &default_domain_tag;
+	if (index_key->type->flags & KEY_TYPE_NET_DOMAIN)
+		index_key->domain_tag = current->nsproxy->net_ns->key_domain;
+	else
+		index_key->domain_tag = &default_domain_tag;
 	hash_key_type_and_desc(index_key);
 }