[RFCv3 00/15] tcp: Initial support for RFC5925 auth option

@@ -140,10 +140,12 @@ struct tcp_request_sock {
 static inline struct tcp_request_sock *tcp_rsk(const struct request_sock *req)
 {
 	return (struct tcp_request_sock *)req;
 }
 
+struct tcp_authopt_info;
+
 struct tcp_sock {
 	/* inet_connection_sock has to be the first member of tcp_sock */
 	struct inet_connection_sock	inet_conn;
 	u16	tcp_header_len;	/* Bytes of tcp header to send		*/
 	u16	gso_segs;	/* Max number of segs per GSO packet	*/

@@ -403,10 +405,14 @@ struct tcp_sock {
 
 /* TCP MD5 Signature Option information */
 	struct tcp_md5sig_info	__rcu *md5sig_info;
 #endif
 
+#ifdef CONFIG_TCP_AUTHOPT
+	struct tcp_authopt_info	__rcu *authopt_info;
+#endif
+
 /* TCP fastopen related information */
 	struct tcp_fastopen_request *fastopen_req;
 	/* fastopen_rsk points to request_sock that resulted in this big
 	 * socket. Used to retransmit SYNACKs etc.
 	 */

@@ -182,10 +182,11 @@ void tcp_time_wait(struct sock *sk, int state, int timeo);
 #define TCPOPT_WINDOW		3	/* Window scaling */
 #define TCPOPT_SACK_PERM        4       /* SACK Permitted */
 #define TCPOPT_SACK             5       /* SACK Block */
 #define TCPOPT_TIMESTAMP	8	/* Better RTT estimations/PAWS */
 #define TCPOPT_MD5SIG		19	/* MD5 Signature (RFC2385) */
+#define TCPOPT_AUTHOPT		29	/* Auth Option (RFC5925) */
 #define TCPOPT_MPTCP		30	/* Multipath TCP (RFC6824) */
 #define TCPOPT_FASTOPEN		34	/* Fast open (RFC7413) */
 #define TCPOPT_EXP		254	/* Experimental */
 /* Magic number to be after the option value for sharing TCP
  * experimental options. See draft-ietf-tcpm-experimental-options-00.txt

@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _LINUX_TCP_AUTHOPT_H
+#define _LINUX_TCP_AUTHOPT_H
+
+#include <uapi/linux/tcp.h>
+
+/**
+ * struct tcp_authopt_key_info - Representation of a Master Key Tuple as per RFC5925
+ *
+ * Key structure lifetime is only protected by RCU so readers needs to hold a
+ * single rcu_read_lock until they're done with the key.
+ */
+struct tcp_authopt_key_info {
+	struct hlist_node node;
+	struct rcu_head rcu;
+	/* Local identifier */
+	u32 local_id;
+	u32 flags;
+	/* Wire identifiers */
+	u8 send_id, recv_id;
+	u8 alg_id;
+	u8 keylen;
+	u8 key[TCP_AUTHOPT_MAXKEYLEN];
+	struct sockaddr_storage addr;
+};
+
+/**
+ * struct tcp_authopt_info - Per-socket information regarding tcp_authopt
+ *
+ * This is lazy-initialized in order to avoid increasing memory usage for
+ * regular TCP sockets. Once created it is only destroyed on socket close.
+ */
+struct tcp_authopt_info {
+	/** @head: List of tcp_authopt_key_info */
+	struct hlist_head head;
+	struct rcu_head rcu;
+	u32 flags;
+	u32 src_isn;
+	u32 dst_isn;
+};
+
+#ifdef CONFIG_TCP_AUTHOPT
+void tcp_authopt_clear(struct sock *sk);
+int tcp_set_authopt(struct sock *sk, sockptr_t optval, unsigned int optlen);
+int tcp_get_authopt_val(struct sock *sk, struct tcp_authopt *key);
+int tcp_set_authopt_key(struct sock *sk, sockptr_t optval, unsigned int optlen);
+#else
+static inline int tcp_set_authopt(struct sock *sk, sockptr_t optval, unsigned int optlen)
+{
+	return -ENOPROTOOPT;
+}
+static inline int tcp_get_authopt_val(struct sock *sk, struct tcp_authopt *key)
+{
+	return -ENOPROTOOPT;
+}
+static inline void tcp_authopt_clear(struct sock *sk)
+{
+}
+static inline int tcp_set_authopt_key(struct sock *sk, sockptr_t optval, unsigned int optlen)
+{
+	return -ENOPROTOOPT;
+}
+#endif
+
+#endif /* _LINUX_TCP_AUTHOPT_H */

@@ -126,10 +126,12 @@ enum {
 #define TCP_INQ			36	/* Notify bytes available to read as a cmsg on read */
 
 #define TCP_CM_INQ		TCP_INQ
 
 #define TCP_TX_DELAY		37	/* delay outgoing packets by XX usec */
+#define TCP_AUTHOPT		38	/* TCP Authentication Option (RFC5925) */
+#define TCP_AUTHOPT_KEY		39	/* TCP Authentication Option Key (RFC5925) */
 
 
 #define TCP_REPAIR_ON		1
 #define TCP_REPAIR_OFF		0
 #define TCP_REPAIR_OFF_NO_WP	-1	/* Turn off without window probes */

@@ -340,10 +342,87 @@ struct tcp_diag_md5sig {
 	__u16	tcpm_keylen;
 	__be32	tcpm_addr[4];
 	__u8	tcpm_key[TCP_MD5SIG_MAXKEYLEN];
 };
 
+/**
+ * enum tcp_authopt_flag - flags for `tcp_authopt.flags`
+ */
+enum tcp_authopt_flag {
+	/**
+	 * @TCP_AUTHOPT_FLAG_REJECT_UNEXPECTED:
+	 *	Configure behavior of segments with TCP-AO coming from hosts for which no
+	 *	key is configured. The default recommended by RFC is to silently accept
+	 *	such connections.
+	 */
+	TCP_AUTHOPT_FLAG_REJECT_UNEXPECTED = (1 << 2),
+};
+
+/**
+ * struct tcp_authopt - Per-socket options related to TCP Authentication Option
+ */
+struct tcp_authopt {
+	/** @flags: Combination of &enum tcp_authopt_flag */
+	__u32	flags;
+};
+
+/**
+ * enum tcp_authopt_key_flag - flags for `tcp_authopt.flags`
+ *
+ * @TCP_AUTHOPT_KEY_DEL: Delete the key by local_id and ignore all other fields.
+ * @TCP_AUTHOPT_KEY_EXCLUDE_OPTS: Exclude TCP options from signature.
+ * @TCP_AUTHOPT_KEY_ADDR_BIND: Key only valid for `tcp_authopt.addr`
+ */
+enum tcp_authopt_key_flag {
+	TCP_AUTHOPT_KEY_DEL = (1 << 0),
+	TCP_AUTHOPT_KEY_EXCLUDE_OPTS = (1 << 1),
+	TCP_AUTHOPT_KEY_ADDR_BIND = (1 << 2),
+};
+
+/**
+ * enum tcp_authopt_alg - Algorithms for TCP Authentication Option
+ */
+enum tcp_authopt_alg {
+	TCP_AUTHOPT_ALG_HMAC_SHA_1_96 = 1,
+	TCP_AUTHOPT_ALG_AES_128_CMAC_96 = 2,
+};
+
+/* for TCP_AUTHOPT_KEY socket option */
+#define TCP_AUTHOPT_MAXKEYLEN	80
+
+/**
+ * struct tcp_authopt_key - TCP Authentication KEY
+ *
+ * Key are identified by the combination of:
+ * - send_id
+ * - recv_id
+ * - addr (iff TCP_AUTHOPT_KEY_ADDR_BIND)
+ *
+ * RFC5925 requires that key ids must not overlap for the same TCP connection.
+ * This is not enforced by linux.
+ */
+struct tcp_authopt_key {
+	/** @flags: Combination of &enum tcp_authopt_key_flag */
+	__u32	flags;
+	/** @send_id: keyid value for send */
+	__u8	send_id;
+	/** @recv_id: keyid value for receive */
+	__u8	recv_id;
+	/** @alg: One of &enum tcp_authopt_alg */
+	__u8	alg;
+	/** @keylen: Length of the key buffer */
+	__u8	keylen;
+	/** @key: Secret key */
+	__u8	key[TCP_AUTHOPT_MAXKEYLEN];
+	/**
+	 * @addr: Key is only valid for this address
+	 *
+	 * Ignored unless TCP_AUTHOPT_KEY_ADDR_BIND flag is set
+	 */
+	struct __kernel_sockaddr_storage addr;
+};
+
 /* setsockopt(fd, IPPROTO_TCP, TCP_ZEROCOPY_RECEIVE, ...) */
 
 #define TCP_RECEIVE_ZEROCOPY_FLAG_TLB_CLEAN_HINT 0x1
 struct tcp_zerocopy_receive {
 	__u64 address;		/* in: address of mapping */

@@ -740,5 +740,19 @@ config TCP_MD5SIG
 	  RFC2385 specifies a method of giving MD5 protection to TCP sessions.
 	  Its main (only?) use is to protect BGP sessions between core routers
 	  on the Internet.
 
 	  If unsure, say N.
+
+config TCP_AUTHOPT
+	bool "TCP: Authentication Option support (RFC5925)"
+	select CRYPTO
+	select CRYPTO_SHA1
+	select CRYPTO_HMAC
+	select CRYPTO_AES
+	select CRYPTO_CMAC
+	help
+	  RFC5925 specifies a new method of giving protection to TCP sessions.
+	  Its intended use is to protect BGP sessions between core routers
+	  on the Internet. It obsoletes TCP MD5 (RFC2385) but is incompatible.
+
+	  If unsure, say N.

@@ -59,10 +59,11 @@ obj-$(CONFIG_TCP_CONG_NV) += tcp_nv.o
 obj-$(CONFIG_TCP_CONG_VENO) += tcp_veno.o
 obj-$(CONFIG_TCP_CONG_SCALABLE) += tcp_scalable.o
 obj-$(CONFIG_TCP_CONG_LP) += tcp_lp.o
 obj-$(CONFIG_TCP_CONG_YEAH) += tcp_yeah.o
 obj-$(CONFIG_TCP_CONG_ILLINOIS) += tcp_illinois.o
+obj-$(CONFIG_TCP_AUTHOPT) += tcp_authopt.o
 obj-$(CONFIG_NET_SOCK_MSG) += tcp_bpf.o
 obj-$(CONFIG_BPF_SYSCALL) += udp_bpf.o
 obj-$(CONFIG_NETLABEL) += cipso_ipv4.o
 
 obj-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \

@@ -271,10 +271,11 @@
 
 #include <net/icmp.h>
 #include <net/inet_common.h>
 #include <net/tcp.h>
 #include <net/mptcp.h>
+#include <net/tcp_authopt.h>
 #include <net/xfrm.h>
 #include <net/ip.h>
 #include <net/sock.h>
 
 #include <linux/uaccess.h>

@@ -3573,10 +3574,16 @@ static int do_tcp_setsockopt(struct sock *sk, int level, int optname,
 	case TCP_MD5SIG:
 	case TCP_MD5SIG_EXT:
 		err = tp->af_specific->md5_parse(sk, optname, optval, optlen);
 		break;
 #endif
+	case TCP_AUTHOPT:
+		err = tcp_set_authopt(sk, optval, optlen);
+		break;
+	case TCP_AUTHOPT_KEY:
+		err = tcp_set_authopt_key(sk, optval, optlen);
+		break;
 	case TCP_USER_TIMEOUT:
 		/* Cap the max time in ms TCP will retry or probe the window
 		 * before giving up and aborting (ETIMEDOUT) a connection.
 		 */
 		if (val < 0)

@@ -4219,10 +4226,30 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
 		if (!err && copy_to_user(optval, &zc, len))
 			err = -EFAULT;
 		return err;
 	}
 #endif
+#ifdef CONFIG_TCP_AUTHOPT
+	case TCP_AUTHOPT: {
+		struct tcp_authopt info;
+
+		if (get_user(len, optlen))
+			return -EFAULT;
+
+		lock_sock(sk);
+		tcp_get_authopt_val(sk, &info);
+		release_sock(sk);
+
+		len = min_t(unsigned int, len, sizeof(info));
+		if (put_user(len, optlen))
+			return -EFAULT;
+		if (copy_to_user(optval, &info, len))
+			return -EFAULT;
+		return 0;
+	}
+#endif
+
 	default:
 		return -ENOPROTOOPT;
 	}
 
 	if (put_user(len, optlen))

@@ -0,0 +1,223 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/kernel.h>
+#include <net/tcp.h>
+#include <net/tcp_authopt.h>
+#include <crypto/hash.h>
+#include <trace/events/tcp.h>
+
+/* checks that ipv4 or ipv6 addr matches. */
+static bool ipvx_addr_match(struct sockaddr_storage *a1,
+			    struct sockaddr_storage *a2)
+{
+	if (a1->ss_family != a2->ss_family)
+		return false;
+	if (a1->ss_family == AF_INET && memcmp(
+			&((struct sockaddr_in *)a1)->sin_addr,
+			&((struct sockaddr_in *)a2)->sin_addr,
+			sizeof(struct in_addr)))
+		return false;
+	if (a1->ss_family == AF_INET6 && memcmp(
+			&((struct sockaddr_in6 *)a1)->sin6_addr,
+			&((struct sockaddr_in6 *)a2)->sin6_addr,
+			sizeof(struct in6_addr)))
+		return false;
+	return true;
+}
+
+static bool tcp_authopt_key_match_exact(struct tcp_authopt_key_info *info,
+					struct tcp_authopt_key *key)
+{
+	if (info->send_id != key->send_id)
+		return false;
+	if (info->recv_id != key->recv_id)
+		return false;
+	if ((info->flags & TCP_AUTHOPT_KEY_ADDR_BIND) != (key->recv_id & TCP_AUTHOPT_KEY_ADDR_BIND))
+		return false;
+	if (info->flags & TCP_AUTHOPT_KEY_ADDR_BIND)
+		if (!ipvx_addr_match(&info->addr, &key->addr))
+			return false;
+
+	return true;
+}
+
+static struct tcp_authopt_key_info *tcp_authopt_key_lookup_exact(const struct sock *sk,
+								 struct tcp_authopt_info *info,
+								 struct tcp_authopt_key *ukey)
+{
+	struct tcp_authopt_key_info *key_info;
+
+	hlist_for_each_entry_rcu(key_info, &info->head, node, lockdep_sock_is_held(sk))
+		if (tcp_authopt_key_match_exact(key_info, ukey))
+			return key_info;
+
+	return NULL;
+}
+
+static struct tcp_authopt_info *__tcp_authopt_info_get_or_create(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct tcp_authopt_info *info;
+
+	info = rcu_dereference_check(tp->authopt_info, lockdep_sock_is_held(sk));
+	if (info)
+		return info;
+
+	info = kmalloc(sizeof(*info), GFP_KERNEL | __GFP_ZERO);
+	if (!info)
+		return ERR_PTR(-ENOMEM);
+
+	sk_nocaps_add(sk, NETIF_F_GSO_MASK);
+	INIT_HLIST_HEAD(&info->head);
+	rcu_assign_pointer(tp->authopt_info, info);
+
+	return info;
+}
+
+#define TCP_AUTHOPT_KNOWN_FLAGS ( \
+	TCP_AUTHOPT_FLAG_REJECT_UNEXPECTED)
+
+int tcp_set_authopt(struct sock *sk, sockptr_t optval, unsigned int optlen)
+{
+	struct tcp_authopt opt;
+	struct tcp_authopt_info *info;
+
+	sock_owned_by_me(sk);
+
+	/* If userspace optlen is too short fill the rest with zeros */
+	if (optlen > sizeof(opt))
+		return -EINVAL;
+	memset(&opt, 0, sizeof(opt));
+	if (copy_from_sockptr(&opt, optval, optlen))
+		return -EFAULT;
+
+	if (opt.flags & ~TCP_AUTHOPT_KNOWN_FLAGS)
+		return -EINVAL;
+
+	info = __tcp_authopt_info_get_or_create(sk);
+	if (IS_ERR(info))
+		return PTR_ERR(info);
+
+	info->flags = opt.flags & TCP_AUTHOPT_KNOWN_FLAGS;
+
+	return 0;
+}
+
+int tcp_get_authopt_val(struct sock *sk, struct tcp_authopt *opt)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct tcp_authopt_info *info;
+
+	sock_owned_by_me(sk);
+
+	memset(opt, 0, sizeof(*opt));
+	info = rcu_dereference_check(tp->authopt_info, lockdep_sock_is_held(sk));
+	if (!info)
+		return -EINVAL;
+
+	opt->flags = info->flags & TCP_AUTHOPT_KNOWN_FLAGS;
+
+	return 0;
+}
+
+static void tcp_authopt_key_del(struct sock *sk,
+				struct tcp_authopt_info *info,
+				struct tcp_authopt_key_info *key)
+{
+	hlist_del_rcu(&key->node);
+	atomic_sub(sizeof(*key), &sk->sk_omem_alloc);
+	kfree_rcu(key, rcu);
+}
+
+/* free info and keys but don't touch tp->authopt_info */
+static void __tcp_authopt_info_free(struct sock *sk, struct tcp_authopt_info *info)
+{
+	struct hlist_node *n;
+	struct tcp_authopt_key_info *key;
+
+	hlist_for_each_entry_safe(key, n, &info->head, node)
+		tcp_authopt_key_del(sk, info, key);
+	kfree_rcu(info, rcu);
+}
+
+/* free everything and clear tcp_sock.authopt_info to NULL */
+void tcp_authopt_clear(struct sock *sk)
+{
+	struct tcp_authopt_info *info;
+
+	info = rcu_dereference_protected(tcp_sk(sk)->authopt_info, lockdep_sock_is_held(sk));
+	if (info) {
+		__tcp_authopt_info_free(sk, info);
+		tcp_sk(sk)->authopt_info = NULL;
+	}
+}
+
+#define TCP_AUTHOPT_KEY_KNOWN_FLAGS ( \
+	TCP_AUTHOPT_KEY_DEL | \
+	TCP_AUTHOPT_KEY_EXCLUDE_OPTS | \
+	TCP_AUTHOPT_KEY_ADDR_BIND)
+
+int tcp_set_authopt_key(struct sock *sk, sockptr_t optval, unsigned int optlen)
+{
+	struct tcp_authopt_key opt;
+	struct tcp_authopt_info *info;
+	struct tcp_authopt_key_info *key_info;
+
+	sock_owned_by_me(sk);
+
+	/* If userspace optlen is too short fill the rest with zeros */
+	if (optlen > sizeof(opt))
+		return -EINVAL;
+	memset(&opt, 0, sizeof(opt));
+	if (copy_from_sockptr(&opt, optval, optlen))
+		return -EFAULT;
+
+	if (opt.flags & ~TCP_AUTHOPT_KEY_KNOWN_FLAGS)
+		return -EINVAL;
+
+	if (opt.keylen > TCP_AUTHOPT_MAXKEYLEN)
+		return -EINVAL;
+
+	/* Delete is a special case: */
+	if (opt.flags & TCP_AUTHOPT_KEY_DEL) {
+		info = rcu_dereference_check(tcp_sk(sk)->authopt_info, lockdep_sock_is_held(sk));
+		if (!info)
+			return -ENOENT;
+		key_info = tcp_authopt_key_lookup_exact(sk, info, &opt);
+		if (!key_info)
+			return -ENOENT;
+		tcp_authopt_key_del(sk, info, key_info);
+		return 0;
+	}
+
+	/* check key family */
+	if (opt.flags & TCP_AUTHOPT_KEY_ADDR_BIND) {
+		if (sk->sk_family != opt.addr.ss_family)
+			return -EINVAL;
+	}
+
+	/* Initialize tcp_authopt_info if not already set */
+	info = __tcp_authopt_info_get_or_create(sk);
+	if (IS_ERR(info))
+		return PTR_ERR(info);
+
+	/* If an old key exists with exact ID then remove and replace.
+	 * RCU-protected readers might observe both and pick any.
+	 */
+	key_info = tcp_authopt_key_lookup_exact(sk, info, &opt);
+	if (key_info)
+		tcp_authopt_key_del(sk, info, key_info);
+	key_info = sock_kmalloc(sk, sizeof(*key_info), GFP_KERNEL | __GFP_ZERO);
+	if (!key_info)
+		return -ENOMEM;
+	key_info->flags = opt.flags & TCP_AUTHOPT_KEY_KNOWN_FLAGS;
+	key_info->send_id = opt.send_id;
+	key_info->recv_id = opt.recv_id;
+	key_info->alg_id = opt.alg;
+	key_info->keylen = opt.keylen;
+	memcpy(key_info->key, opt.key, opt.keylen);
+	memcpy(&key_info->addr, &opt.addr, sizeof(key_info->addr));
+	hlist_add_head_rcu(&key_info->node, &info->head);
+
+	return 0;
+}

@@ -60,10 +60,11 @@
 
 #include <net/net_namespace.h>
 #include <net/icmp.h>
 #include <net/inet_hashtables.h>
 #include <net/tcp.h>
+#include <net/tcp_authopt.h>
 #include <net/transp_v6.h>
 #include <net/ipv6.h>
 #include <net/inet_common.h>
 #include <net/timewait_sock.h>
 #include <net/xfrm.h>

@@ -2256,10 +2257,11 @@ void tcp_v4_destroy_sock(struct sock *sk)
 		tcp_clear_md5_list(sk);
 		kfree_rcu(rcu_dereference_protected(tp->md5sig_info, 1), rcu);
 		tp->md5sig_info = NULL;
 	}
 #endif
+	tcp_authopt_clear(sk);
 
 	/* Clean up a referenced TCP bind bucket. */
 	if (inet_csk(sk)->icsk_bind_hash)
 		inet_put_port(sk);
 

@@ -100,10 +100,11 @@ Contents:
    strparser
    switchdev
    sysfs-tagging
    tc-actions-env-rules
    tcp-thin
+   tcp_authopt
    team
    timestamping
    tipc
    tproxy
    tuntap

@@ -0,0 +1,44 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=========================
+TCP Authentication Option
+=========================
+
+The TCP Authentication option specified by RFC5925 replaces the TCP MD5
+Signature option. It similar in goals but not compatible in either wire formats
+or ABI.
+
+Interface
+=========
+
+Individual keys can be added to or removed from a TCP socket by using
+TCP_AUTHOPT_KEY setsockopt and a ``struct tcp_authopt_key``. There is no
+support for reading back keys and updates always replace the old key. These
+structures represent "Master Key Tuples (MKTs)" as described by the RFC.
+
+Per-socket options can set or read using the TCP_AUTHOPT sockopt and a ``struct
+tcp_authopt``. This is optional: doing setsockopt TCP_AUTHOPT_KEY is
+sufficient to enable the feature.
+
+Configuration associated with TCP Authentication is indepedently attached to
+each TCP socket. After listen and accept the newly returned socket gets an
+independent copy of relevant settings from the listen socket.
+
+Key binding
+-----------
+
+Keys can be bound to remote addresses in a way that is similar to TCP_MD5.
+
+ * The full address must match (/32 or /128)
+ * Ports are ignored
+ * Address binding is optional, by default keys match all addresses
+
+RFC5925 requires that key ids do not overlap when tcp identifiers (addr/port)
+overlap. This is not enforced by linux, configuring ambiguous keys will result
+in packet drops and lost connections.
+
+ABI Reference
+=============
+
+.. kernel-doc:: include/uapi/linux/tcp.h
+   :identifiers: tcp_authopt tcp_authopt_flag tcp_authopt_key tcp_authopt_key_flag tcp_authopt_alg

@@ -2,10 +2,12 @@
 #ifndef _LINUX_TCP_AUTHOPT_H
 #define _LINUX_TCP_AUTHOPT_H
 
 #include <uapi/linux/tcp.h>
 
+struct tcp_authopt_alg_imp;
+
 /**
  * struct tcp_authopt_key_info - Representation of a Master Key Tuple as per RFC5925
  *
  * Key structure lifetime is only protected by RCU so readers needs to hold a
  * single rcu_read_lock until they're done with the key.

@@ -20,10 +22,11 @@ struct tcp_authopt_key_info {
 	u8 send_id, recv_id;
 	u8 alg_id;
 	u8 keylen;
 	u8 key[TCP_AUTHOPT_MAXKEYLEN];
 	struct sockaddr_storage addr;
+	struct tcp_authopt_alg_imp *alg;
 };
 
 /**
  * struct tcp_authopt_info - Per-socket information regarding tcp_authopt
  *

@@ -4,10 +4,161 @@
 #include <net/tcp.h>
 #include <net/tcp_authopt.h>
 #include <crypto/hash.h>
 #include <trace/events/tcp.h>
 
+/* All current algorithms have a mac length of 12 but crypto API digestsize can be larger */
+#define TCP_AUTHOPT_MAXMACBUF	20
+#define TCP_AUTHOPT_MAX_TRAFFIC_KEY_LEN	20
+
+struct tcp_authopt_alg_imp {
+	/* Name of algorithm in crypto-api */
+	const char *alg_name;
+	/* One of the TCP_AUTHOPT_ALG_* constants from uapi */
+	u8 alg_id;
+	/* Length of traffic key */
+	u8 traffic_key_len;
+	/* Length of mac in TCP option */
+	u8 maclen;
+
+	/* shared crypto_shash */
+	spinlock_t lock;
+	int ref_cnt;
+	struct crypto_shash *tfm;
+};
+
+static struct tcp_authopt_alg_imp tcp_authopt_alg_list[] = {
+	{
+		.alg_id = TCP_AUTHOPT_ALG_HMAC_SHA_1_96,
+		.alg_name = "hmac(sha1)",
+		.traffic_key_len = 20,
+		.maclen = 12,
+		.lock = __SPIN_LOCK_UNLOCKED(tcp_authopt_alg_list[0].lock),
+	},
+	{
+		.alg_id = TCP_AUTHOPT_ALG_AES_128_CMAC_96,
+		.alg_name = "cmac(aes)",
+		.traffic_key_len = 16,
+		.maclen = 12,
+		.lock = __SPIN_LOCK_UNLOCKED(tcp_authopt_alg_list[1].lock),
+	},
+};
+
+/* get a pointer to the tcp_authopt_alg instance or NULL if id invalid */
+static inline struct tcp_authopt_alg_imp *tcp_authopt_alg_get(int alg_num)
+{
+	if (alg_num <= 0 || alg_num > 2)
+		return NULL;
+	return &tcp_authopt_alg_list[alg_num - 1];
+}
+
+/* Mark an algorithm as in-use from user context */
+static int tcp_authopt_alg_require(struct tcp_authopt_alg_imp *alg)
+{
+	struct crypto_shash *tfm = NULL;
+	bool need_init = false;
+
+	might_sleep();
+
+	/* If we're the first user then we need to initialize shash but we might lose the race. */
+	spin_lock_bh(&alg->lock);
+	WARN_ON(alg->ref_cnt < 0);
+	if (alg->ref_cnt == 0)
+		need_init = true;
+	else
+		++alg->ref_cnt;
+	spin_unlock_bh(&alg->lock);
+
+	/* Already initialized */
+	if (!need_init)
+		return 0;
+
+	tfm = crypto_alloc_shash(alg->alg_name, 0, 0);
+	if (IS_ERR(tfm))
+		return PTR_ERR(tfm);
+
+	spin_lock_bh(&alg->lock);
+	if (alg->ref_cnt == 0)
+		/* race won */
+		alg->tfm = tfm;
+	else
+		/* race lost, free tfm later */
+		need_init = false;
+	++alg->ref_cnt;
+	spin_unlock_bh(&alg->lock);
+
+	if (!need_init)
+		crypto_free_shash(tfm);
+	else
+		pr_info("initialized tcp-ao %s", alg->alg_name);
+
+	return 0;
+}
+
+static void tcp_authopt_alg_release(struct tcp_authopt_alg_imp *alg)
+{
+	struct crypto_shash *tfm_to_free = NULL;
+
+	spin_lock_bh(&alg->lock);
+	--alg->ref_cnt;
+	WARN_ON(alg->ref_cnt < 0);
+	if (alg->ref_cnt == 0) {
+		tfm_to_free = alg->tfm;
+		alg->tfm = NULL;
+	}
+	spin_unlock_bh(&alg->lock);
+
+	if (tfm_to_free) {
+		pr_info("released tcp-ao %s", alg->alg_name);
+		crypto_free_shash(tfm_to_free);
+	}
+}
+
+/* increase reference count on an algorithm that is already in use */
+static void tcp_authopt_alg_incref(struct tcp_authopt_alg_imp *alg)
+{
+	spin_lock_bh(&alg->lock);
+	WARN_ON(alg->ref_cnt <= 0);
+	++alg->ref_cnt;
+	spin_unlock_bh(&alg->lock);
+}
+
+static struct crypto_shash *tcp_authopt_alg_get_tfm(struct tcp_authopt_alg_imp *alg)
+{
+	spin_lock_bh(&alg->lock);
+	WARN_ON(alg->ref_cnt < 0);
+	return alg->tfm;
+}
+
+static void tcp_authopt_alg_put_tfm(struct tcp_authopt_alg_imp *alg, struct crypto_shash *tfm)
+{
+	WARN_ON(tfm != alg->tfm);
+	spin_unlock_bh(&alg->lock);
+}
+
+static struct crypto_shash *tcp_authopt_get_kdf_shash(struct tcp_authopt_key_info *key)
+{
+	return tcp_authopt_alg_get_tfm(key->alg);
+}
+
+static void tcp_authopt_put_kdf_shash(struct tcp_authopt_key_info *key,
+				      struct crypto_shash *tfm)
+{
+	return tcp_authopt_alg_put_tfm(key->alg, tfm);
+}
+
+static struct crypto_shash *tcp_authopt_get_mac_shash(struct tcp_authopt_key_info *key)
+{
+	return tcp_authopt_alg_get_tfm(key->alg);
+}
+
+static void tcp_authopt_put_mac_shash(struct tcp_authopt_key_info *key,
+				      struct crypto_shash *tfm)
+{
+	return tcp_authopt_alg_put_tfm(key->alg, tfm);
+}
+
 /* checks that ipv4 or ipv6 addr matches. */
 static bool ipvx_addr_match(struct sockaddr_storage *a1,
 			    struct sockaddr_storage *a2)
 {
 	if (a1->ss_family != a2->ss_family)

@@ -118,17 +269,25 @@ int tcp_get_authopt_val(struct sock *sk, struct tcp_authopt *opt)
 	opt->flags = info->flags & TCP_AUTHOPT_KNOWN_FLAGS;
 
 	return 0;
 }
 
+static void tcp_authopt_key_free_rcu(struct rcu_head *rcu)
+{
+	struct tcp_authopt_key_info *key = container_of(rcu, struct tcp_authopt_key_info, rcu);
+
+	tcp_authopt_alg_release(key->alg);
+	kfree(key);
+}
+
 static void tcp_authopt_key_del(struct sock *sk,
 				struct tcp_authopt_info *info,
 				struct tcp_authopt_key_info *key)
 {
 	hlist_del_rcu(&key->node);
 	atomic_sub(sizeof(*key), &sk->sk_omem_alloc);
-	kfree_rcu(key, rcu);
+	call_rcu(&key->rcu, tcp_authopt_key_free_rcu);
 }
 
 /* free info and keys but don't touch tp->authopt_info */
 static void __tcp_authopt_info_free(struct sock *sk, struct tcp_authopt_info *info)
 {

@@ -160,10 +319,12 @@ void tcp_authopt_clear(struct sock *sk)
 int tcp_set_authopt_key(struct sock *sk, sockptr_t optval, unsigned int optlen)
 {
 	struct tcp_authopt_key opt;
 	struct tcp_authopt_info *info;
 	struct tcp_authopt_key_info *key_info;
+	struct tcp_authopt_alg_imp *alg;
+	int err;
 
 	sock_owned_by_me(sk);
 
 	/* If userspace optlen is too short fill the rest with zeros */
 	if (optlen > sizeof(opt))

@@ -199,23 +360,35 @@ int tcp_set_authopt_key(struct sock *sk, sockptr_t optval, unsigned int optlen)
 	/* Initialize tcp_authopt_info if not already set */
 	info = __tcp_authopt_info_get_or_create(sk);
 	if (IS_ERR(info))
 		return PTR_ERR(info);
 
+	/* check the algorithm */
+	alg = tcp_authopt_alg_get(opt.alg);
+	if (!alg)
+		return -EINVAL;
+	WARN_ON(alg->alg_id != opt.alg);
+	err = tcp_authopt_alg_require(alg);
+	if (err)
+		return err;
+
 	/* If an old key exists with exact ID then remove and replace.
 	 * RCU-protected readers might observe both and pick any.
 	 */
 	key_info = tcp_authopt_key_lookup_exact(sk, info, &opt);
 	if (key_info)
 		tcp_authopt_key_del(sk, info, key_info);
 	key_info = sock_kmalloc(sk, sizeof(*key_info), GFP_KERNEL | __GFP_ZERO);
-	if (!key_info)
+	if (!key_info) {
+		tcp_authopt_alg_release(alg);
 		return -ENOMEM;
+	}
 	key_info->flags = opt.flags & TCP_AUTHOPT_KEY_KNOWN_FLAGS;
 	key_info->send_id = opt.send_id;
 	key_info->recv_id = opt.recv_id;
 	key_info->alg_id = opt.alg;
+	key_info->alg = alg;
 	key_info->keylen = opt.keylen;
 	memcpy(key_info->key, opt.key, opt.keylen);
 	memcpy(&key_info->addr, &opt.addr, sizeof(key_info->addr));
 	hlist_add_head_rcu(&key_info->node, &info->head);
 

@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+include ../lib.mk
+
+TEST_PROGS += ./run.sh
+TEST_FILES := setup.py setup.cfg tcp_authopt_test

@@ -0,0 +1,15 @@
+=========================================
+Tests for linux TCP Authentication Option
+=========================================
+
+Test suite is written in python3 using pytest and scapy. The test suite is
+mostly self-contained as a python package.
+
+The recommended way to run this is the included `run.sh` script as root, this
+will automatically create a virtual environment with the correct dependencies
+using `tox`.
+
+An old separate version can be found here: https://github.com/cdleonard/tcp-authopt-test
+
+Integration with kselftest infrastructure is minimal: when in doubt just run
+this separately.

@@ -0,0 +1,6 @@
+# RFC5925 TCP Authentication Option and all algorithms
+CONFIG_TCP_AUTHOPT=y
+CONFIG_CRYPTO_SHA1=M
+CONFIG_CRYPTO_HMAC=M
+CONFIG_CRYPTO_AES=M
+CONFIG_CRYPTO_CMAC=M

@@ -0,0 +1,11 @@
+#! /bin/bash
+
+if ! command -v tox >/dev/null; then
+	echo >&2 "error: please install the python tox package"
+	exit 1
+fi
+if [[ $(id -u) -ne 0 ]]; then
+	echo >&2 "warning: running as non-root user is unlikely to work"
+fi
+cd "$(dirname "${BASH_SOURCE[0]}")"
+exec tox "$@"

@@ -0,0 +1,17 @@
+[options]
+install_requires=
+    cryptography
+    nsenter
+    pre-commit
+    pytest
+    scapy
+
+[tox:tox]
+envlist = py3
+
+[testenv]
+commands = pytest {posargs}
+
+[metadata]
+name = tcp-authopt-test
+version = 0.1

@@ -0,0 +1,5 @@
+#! /usr/bin/env python3
+
+from setuptools import setup
+
+setup()

@@ -0,0 +1,21 @@
+# SPDX-License-Identifier: GPL-2.0
+from tcp_authopt_test.linux_tcp_authopt import has_tcp_authopt
+import pytest
+import logging
+from contextlib import ExitStack
+
+logger = logging.getLogger(__name__)
+
+skipif_missing_tcp_authopt = pytest.mark.skipif(
+    not has_tcp_authopt(), reason="Need CONFIG_TCP_AUTHOPT"
+)
+
+
+@pytest.fixture
+def exit_stack():
+    """Return a contextlib.ExitStack as a pytest fixture
+
+    This reduces indentation making code more readable
+    """
+    with ExitStack() as exit_stack:
+        yield exit_stack

@@ -0,0 +1,188 @@
+# SPDX-License-Identifier: GPL-2.0
+"""Python wrapper around linux TCP_AUTHOPT ABI"""
+
+from dataclasses import dataclass
+from ipaddress import IPv4Address, IPv6Address, ip_address
+import socket
+import errno
+import logging
+from .sockaddr import sockaddr_in, sockaddr_in6, sockaddr_storage, sockaddr_unpack
+import typing
+import struct
+
+logger = logging.getLogger(__name__)
+
+
+def BIT(x):
+    return 1 << x
+
+
+TCP_AUTHOPT = 38
+TCP_AUTHOPT_KEY = 39
+
+TCP_AUTHOPT_MAXKEYLEN = 80
+
+TCP_AUTHOPT_FLAG_REJECT_UNEXPECTED = BIT(2)
+
+TCP_AUTHOPT_KEY_DEL = BIT(0)
+TCP_AUTHOPT_KEY_EXCLUDE_OPTS = BIT(1)
+TCP_AUTHOPT_KEY_BIND_ADDR = BIT(2)
+
+TCP_AUTHOPT_ALG_HMAC_SHA_1_96 = 1
+TCP_AUTHOPT_ALG_AES_128_CMAC_96 = 2
+
+
+@dataclass
+class tcp_authopt:
+    """Like linux struct tcp_authopt"""
+
+    flags: int = 0
+    sizeof = 4
+
+    def pack(self) -> bytes:
+        return struct.pack(
+            "I",
+            self.flags,
+        )
+
+    def __bytes__(self):
+        return self.pack()
+
+    @classmethod
+    def unpack(cls, b: bytes):
+        tup = struct.unpack("I", b)
+        return cls(*tup)
+
+
+def set_tcp_authopt(sock, opt: tcp_authopt):
+    return sock.setsockopt(socket.IPPROTO_TCP, TCP_AUTHOPT, bytes(opt))
+
+
+def get_tcp_authopt(sock: socket.socket) -> tcp_authopt:
+    b = sock.getsockopt(socket.IPPROTO_TCP, TCP_AUTHOPT, tcp_authopt.sizeof)
+    return tcp_authopt.unpack(b)
+
+
+class tcp_authopt_key:
+    """Like linux struct tcp_authopt_key"""
+
+    def __init__(
+        self,
+        flags: int = 0,
+        send_id: int = 0,
+        recv_id: int = 0,
+        alg=TCP_AUTHOPT_ALG_HMAC_SHA_1_96,
+        key: bytes = b"",
+        addr: bytes = b"",
+        include_options=None,
+    ):
+        self.flags = flags
+        self.send_id = send_id
+        self.recv_id = recv_id
+        self.alg = alg
+        self.key = key
+        self.addr = addr
+        if include_options is not None:
+            self.include_options = include_options
+
+    def pack(self):
+        if len(self.key) > TCP_AUTHOPT_MAXKEYLEN:
+            raise ValueError(f"Max key length is {TCP_AUTHOPT_MAXKEYLEN}")
+        data = struct.pack(
+            "IBBBB80s",
+            self.flags,
+            self.send_id,
+            self.recv_id,
+            self.alg,
+            len(self.key),
+            self.key,
+        )
+        data += bytes(self.addrbuf.ljust(sockaddr_storage.sizeof, b"\x00"))
+        return data
+
+    def __bytes__(self):
+        return self.pack()
+
+    @property
+    def key(self) -> bytes:
+        return self._key
+
+    @key.setter
+    def key(self, val: typing.Union[bytes, str]) -> bytes:
+        if isinstance(val, str):
+            val = val.encode("utf-8")
+        if len(val) > TCP_AUTHOPT_MAXKEYLEN:
+            raise ValueError(f"Max key length is {TCP_AUTHOPT_MAXKEYLEN}")
+        self._key = val
+        return val
+
+    @property
+    def addr(self):
+        if not self.addrbuf:
+            return None
+        else:
+            return sockaddr_unpack(bytes(self.addrbuf))
+
+    @addr.setter
+    def addr(self, val):
+        if isinstance(val, bytes):
+            if len(val) > sockaddr_storage.sizeof:
+                raise ValueError(f"Must be up to {sockaddr_storage.sizeof}")
+            self.addrbuf = val
+        elif val is None:
+            self.addrbuf = b""
+        elif isinstance(val, str):
+            self.addr = ip_address(val)
+        elif isinstance(val, IPv4Address):
+            self.addr = sockaddr_in(addr=val)
+        elif isinstance(val, IPv6Address):
+            self.addr = sockaddr_in6(addr=val)
+        elif (
+            isinstance(val, sockaddr_in)
+            or isinstance(val, sockaddr_in6)
+            or isinstance(val, sockaddr_storage)
+        ):
+            self.addr = bytes(val)
+        else:
+            raise TypeError(f"Can't handle addr {val}")
+        return self.addr
+
+    @property
+    def include_options(self) -> bool:
+        return (self.flags & TCP_AUTHOPT_KEY_EXCLUDE_OPTS) == 0
+
+    @include_options.setter
+    def include_options(self, value) -> bool:
+        if value:
+            self.flags &= ~TCP_AUTHOPT_KEY_EXCLUDE_OPTS
+        else:
+            self.flags |= TCP_AUTHOPT_KEY_EXCLUDE_OPTS
+
+    @property
+    def delete_flag(self) -> bool:
+        return bool(self.flags & TCP_AUTHOPT_KEY_DEL)
+
+    @delete_flag.setter
+    def delete_flag(self, value) -> bool:
+        if value:
+            self.flags |= TCP_AUTHOPT_KEY_DEL
+        else:
+            self.flags &= ~TCP_AUTHOPT_KEY_DEL
+
+
+def set_tcp_authopt_key(sock, key: tcp_authopt_key):
+    return sock.setsockopt(socket.IPPROTO_TCP, TCP_AUTHOPT_KEY, bytes(key))
+
+
+def has_tcp_authopt() -> bool:
+    """Check is TCP_AUTHOPT is implemented by the OS"""
+    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
+        try:
+            optbuf = bytes(4)
+            sock.setsockopt(socket.IPPROTO_TCP, TCP_AUTHOPT, optbuf)
+            return True
+        except OSError as e:
+            if e.errno == errno.ENOPROTOOPT:
+                return False
+            else:
+                raise