crypto: user - make NETLINK_CRYPTO work inside netns

Currently, NETLINK_CRYPTO works only in the init network namespace. It
doesn't make much sense to cut it out of the other network namespaces,
so do the minor plumbing work necessary to make it work in any network
namespace. Code inspired by net/core/sock_diag.c.

Tested using kcapi-dgst from libkcapi [1]:
Before:
    # unshare -n kcapi-dgst -c sha256 </dev/null | wc -c
    libkcapi - Error: Netlink error: sendmsg failed
    libkcapi - Error: Netlink error: sendmsg failed
    libkcapi - Error: NETLINK_CRYPTO: cannot obtain cipher information for hmac(sha512) (is required crypto_user.c patch missing? see documentation)
    0

After:
    # unshare -n kcapi-dgst -c sha256 </dev/null | wc -c
    32

[1] https://github.com/smuellerDD/libkcapiSigned-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/crypto_user_base.c

@@ -10,9 +10,10 @@
 #include <linux/crypto.h>
 #include <linux/cryptouser.h>
 #include <linux/sched.h>
-#include <net/netlink.h>
 #include <linux/security.h>
+#include <net/netlink.h>
 #include <net/net_namespace.h>
+#include <net/sock.h>
 #include <crypto/internal/skcipher.h>
 #include <crypto/internal/rng.h>
 #include <crypto/akcipher.h>
@@ -25,9 +26,6 @@
 
 static DEFINE_MUTEX(crypto_cfg_mutex);
 
-/* The crypto netlink socket */
-struct sock *crypto_nlsk;
-
 struct crypto_dump_info {
 	struct sk_buff *in_skb;
 	struct sk_buff *out_skb;
@@ -186,6 +184,7 @@ static int crypto_report_alg(struct crypto_alg *alg,
 static int crypto_report(struct sk_buff *in_skb, struct nlmsghdr *in_nlh,
 			 struct nlattr **attrs)
 {
+	struct net *net = sock_net(in_skb->sk);
 	struct crypto_user_alg *p = nlmsg_data(in_nlh);
 	struct crypto_alg *alg;
 	struct sk_buff *skb;
@@ -217,7 +216,7 @@ static int crypto_report(struct sk_buff *in_skb, struct nlmsghdr *in_nlh,
 	if (err)
 		return err;
 
-	return nlmsg_unicast(crypto_nlsk, skb, NETLINK_CB(in_skb).portid);
+	return nlmsg_unicast(net->crypto_nlsk, skb, NETLINK_CB(in_skb).portid);
 }
 
 static int crypto_dump_report(struct sk_buff *skb, struct netlink_callback *cb)
@@ -420,6 +419,7 @@ static const struct crypto_link {
 static int crypto_user_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
 			       struct netlink_ext_ack *extack)
 {
+	struct net *net = sock_net(skb->sk);
 	struct nlattr *attrs[CRYPTOCFGA_MAX+1];
 	const struct crypto_link *link;
 	int type, err;
@@ -450,7 +450,7 @@ static int crypto_user_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
 				.done = link->done,
 				.min_dump_alloc = min(dump_alloc, 65535UL),
 			};
-			err = netlink_dump_start(crypto_nlsk, skb, nlh, &c);
+			err = netlink_dump_start(net->crypto_nlsk, skb, nlh, &c);
 		}
 
 		return err;
@@ -474,22 +474,35 @@ static void crypto_netlink_rcv(struct sk_buff *skb)
 	mutex_unlock(&crypto_cfg_mutex);
 }
 
-static int __init crypto_user_init(void)
+static int __net_init crypto_netlink_init(struct net *net)
 {
 	struct netlink_kernel_cfg cfg = {
 		.input	= crypto_netlink_rcv,
 	};
 
-	crypto_nlsk = netlink_kernel_create(&init_net, NETLINK_CRYPTO, &cfg);
-	if (!crypto_nlsk)
-		return -ENOMEM;
+	net->crypto_nlsk = netlink_kernel_create(net, NETLINK_CRYPTO, &cfg);
+	return net->crypto_nlsk == NULL ? -ENOMEM : 0;
+}
 
-	return 0;
+static void __net_exit crypto_netlink_exit(struct net *net)
+{
+	netlink_kernel_release(net->crypto_nlsk);
+	net->crypto_nlsk = NULL;
+}
+
+static struct pernet_operations crypto_netlink_net_ops = {
+	.init = crypto_netlink_init,
+	.exit = crypto_netlink_exit,
+};
+
+static int __init crypto_user_init(void)
+{
+	return register_pernet_subsys(&crypto_netlink_net_ops);
 }
 
 static void __exit crypto_user_exit(void)
 {
-	netlink_kernel_release(crypto_nlsk);
+	unregister_pernet_subsys(&crypto_netlink_net_ops);
 }
 
 module_init(crypto_user_init);

crypto/crypto_user_stat.c

@@ -10,6 +10,7 @@
 #include <linux/cryptouser.h>
 #include <linux/sched.h>
 #include <net/netlink.h>
+#include <net/sock.h>
 #include <crypto/internal/skcipher.h>
 #include <crypto/internal/rng.h>
 #include <crypto/akcipher.h>
@@ -298,6 +299,7 @@ static int crypto_reportstat_alg(struct crypto_alg *alg,
 int crypto_reportstat(struct sk_buff *in_skb, struct nlmsghdr *in_nlh,
 		      struct nlattr **attrs)
 {
+	struct net *net = sock_net(in_skb->sk);
 	struct crypto_user_alg *p = nlmsg_data(in_nlh);
 	struct crypto_alg *alg;
 	struct sk_buff *skb;
@@ -329,7 +331,7 @@ int crypto_reportstat(struct sk_buff *in_skb, struct nlmsghdr *in_nlh,
 	if (err)
 		return err;
 
-	return nlmsg_unicast(crypto_nlsk, skb, NETLINK_CB(in_skb).portid);
+	return nlmsg_unicast(net->crypto_nlsk, skb, NETLINK_CB(in_skb).portid);
 }
 
 MODULE_LICENSE("GPL");

include/crypto/internal/cryptouser.h

 /* SPDX-License-Identifier: GPL-2.0 */
 #include <net/netlink.h>
 
-extern struct sock *crypto_nlsk;
-
 struct crypto_alg *crypto_alg_match(struct crypto_user_alg *p, int exact);
 
 #ifdef CONFIG_CRYPTO_STATS

include/net/net_namespace.h

@@ -170,6 +170,9 @@ struct net {
 #endif
 #ifdef CONFIG_XDP_SOCKETS
 	struct netns_xdp	xdp;
+#endif
+#if IS_ENABLED(CONFIG_CRYPTO_USER)
+	struct sock		*crypto_nlsk;
 #endif
 	struct sock		*diag_nlsk;
 	atomic_t		fnhe_genid;