net/tcp: Introduce TCP_AO setsockopt()s

Add 3 setsockopt()s:
1. TCP_AO_ADD_KEY to add a new Master Key Tuple (MKT) on a socket
2. TCP_AO_DEL_KEY to delete present MKT from a socket
3. TCP_AO_INFO to change flags, Current_key/RNext_key on a TCP-AO sk

Userspace has to introduce keys on every socket it wants to use TCP-AO
option on, similarly to TCP_MD5SIG/TCP_MD5SIG_EXT.
RFC5925 prohibits definition of MKTs that would match the same peer,
so do sanity checks on the data provided by userspace. Be as
conservative as possible, including refusal of defining MKT on
an established connection with no AO, removing the key in-use and etc.

(1) and (2) are to be used by userspace key manager to add/remove keys.
(3) main purpose is to set RNext_key, which (as prescribed by RFC5925)
is the KeyID that will be requested in TCP-AO header from the peer to
sign their segments with.

At this moment the life of ao_info ends in tcp_v4_destroy_sock().

Co-developed-by: Francesco Ruggeri <[e-mail]>
Signed-off-by: Francesco Ruggeri <[e-mail]>
Co-developed-by: Salam Noureddine <[e-mail]>
Signed-off-by: Salam Noureddine <[e-mail]>
Signed-off-by: Dmitry Safonov <[e-mail]>
Acked-by: David Ahern <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/sockptr.h

···
 	return copy_from_sockptr_offset(dst, src, 0, size);
 }
 
+static inline int copy_struct_from_sockptr(void *dst, size_t ksize,
+		sockptr_t src, size_t usize)
+{
+	size_t size = min(ksize, usize);
+	size_t rest = max(ksize, usize) - size;
+
+	if (!sockptr_is_kernel(src))
+		return copy_struct_from_user(dst, ksize, src.user, size);
+
+	if (usize < ksize) {
+		memset(dst + size, 0, rest);
+	} else if (usize > ksize) {
+		char *p = src.kernel;
+
+		while (rest--) {
+			if (*p++)
+				return -E2BIG;
+		}
+	}
+	memcpy(dst, src.kernel, size);
+	return 0;
+}
+
 static inline int copy_to_sockptr_offset(sockptr_t dst, size_t offset,
 		const void *src, size_t size)
 {

include/net/tcp.h

···
 				     sockptr_t optval,
 				     int optlen);
 #endif
+#ifdef CONFIG_TCP_AO
+	int (*ao_parse)(struct sock *sk, int optname, sockptr_t optval, int optlen);
+#endif
 };
 
 struct tcp_request_sock_ops {

include/net/tcp_ao.h

···
 	 */
 	struct tcp_ao_key	*current_key;
 	struct tcp_ao_key	*rnext_key;
-	u32			flags;
+	u32			ao_required	:1,
+				__unused	:31;
 	__be32			lisn;
 	__be32			risn;
 	struct rcu_head		rcu;
 };
+
+#ifdef CONFIG_TCP_AO
+int tcp_parse_ao(struct sock *sk, int cmd, unsigned short int family,
+		 sockptr_t optval, int optlen);
+void tcp_ao_destroy_sock(struct sock *sk);
+/* ipv4 specific functions */
+int tcp_v4_parse_ao(struct sock *sk, int cmd, sockptr_t optval, int optlen);
+/* ipv6 specific functions */
+int tcp_v6_parse_ao(struct sock *sk, int cmd, sockptr_t optval, int optlen);
+#else
+static inline void tcp_ao_destroy_sock(struct sock *sk)
+{
+}
+#endif
 
 #endif /* _TCP_AO_H */

include/uapi/linux/tcp.h

···
 
 #define TCP_TX_DELAY		37	/* delay outgoing packets by XX usec */
 
+#define TCP_AO_ADD_KEY		38	/* Add/Set MKT */
+#define TCP_AO_DEL_KEY		39	/* Delete MKT */
+#define TCP_AO_INFO		40	/* Modify TCP-AO per-socket options */
 
 #define TCP_REPAIR_ON		1
 #define TCP_REPAIR_OFF		0
···
 };
 
 #define TCP_AO_MAXKEYLEN	80
+
+#define TCP_AO_KEYF_IFINDEX	(1 << 0)	/* L3 ifindex for VRF */
+
+struct tcp_ao_add { /* setsockopt(TCP_AO_ADD_KEY) */
+	struct __kernel_sockaddr_storage addr;	/* peer's address for the key */
+	char	alg_name[64];		/* crypto hash algorithm to use */
+	__s32	ifindex;		/* L3 dev index for VRF */
+	__u32   set_current	:1,	/* set key as Current_key at once */
+		set_rnext	:1,	/* request it from peer with RNext_key */
+		reserved	:30;	/* must be 0 */
+	__u16	reserved2;		/* padding, must be 0 */
+	__u8	prefix;			/* peer's address prefix */
+	__u8	sndid;			/* SendID for outgoing segments */
+	__u8	rcvid;			/* RecvID to match for incoming seg */
+	__u8	maclen;			/* length of authentication code (hash) */
+	__u8	keyflags;		/* see TCP_AO_KEYF_ */
+	__u8	keylen;			/* length of ::key */
+	__u8	key[TCP_AO_MAXKEYLEN];
+} __attribute__((aligned(8)));
+
+struct tcp_ao_del { /* setsockopt(TCP_AO_DEL_KEY) */
+	struct __kernel_sockaddr_storage addr;	/* peer's address for the key */
+	__s32	ifindex;		/* L3 dev index for VRF */
+	__u32   set_current	:1,	/* corresponding ::current_key */
+		set_rnext	:1,	/* corresponding ::rnext */
+		reserved	:30;	/* must be 0 */
+	__u16	reserved2;		/* padding, must be 0 */
+	__u8	prefix;			/* peer's address prefix */
+	__u8	sndid;			/* SendID for outgoing segments */
+	__u8	rcvid;			/* RecvID to match for incoming seg */
+	__u8	current_key;		/* KeyID to set as Current_key */
+	__u8	rnext;			/* KeyID to set as Rnext_key */
+	__u8	keyflags;		/* see TCP_AO_KEYF_ */
+} __attribute__((aligned(8)));
+
+struct tcp_ao_info_opt { /* setsockopt(TCP_AO_INFO) */
+	__u32   set_current	:1,	/* corresponding ::current_key */
+		set_rnext	:1,	/* corresponding ::rnext */
+		ao_required	:1,	/* don't accept non-AO connects */
+		reserved	:29;	/* must be 0 */
+	__u8	current_key;		/* KeyID to set as Current_key */
+	__u8	rnext;			/* KeyID to set as Rnext_key */
+} __attribute__((aligned(8)));
 
 /* setsockopt(fd, IPPROTO_TCP, TCP_ZEROCOPY_RECEIVE, ...) */
 

net/ipv4/Makefile

···
 
 obj-$(CONFIG_XFRM) += xfrm4_policy.o xfrm4_state.o xfrm4_input.o \
 		      xfrm4_output.o xfrm4_protocol.o
+obj-$(CONFIG_TCP_AO) += tcp_ao.o
 
 ifeq ($(CONFIG_BPF_JIT),y)
 obj-$(CONFIG_BPF_SYSCALL) += bpf_tcp_ca.o

net/ipv4/tcp.c

···
 		__tcp_sock_set_quickack(sk, val);
 		break;
 
+#ifdef CONFIG_TCP_AO
+	case TCP_AO_ADD_KEY:
+	case TCP_AO_DEL_KEY:
+	case TCP_AO_INFO: {
+		/* If this is the first TCP-AO setsockopt() on the socket,
+		 * sk_state has to be LISTEN or CLOSE
+		 */
+		if (((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE)) ||
+		    rcu_dereference_protected(tcp_sk(sk)->ao_info,
+					      lockdep_sock_is_held(sk)))
+			err = tp->af_specific->ao_parse(sk, optname, optval,
+							optlen);
+		else
+			err = -EISCONN;
+		break;
+	}
+#endif
 #ifdef CONFIG_TCP_MD5SIG
 	case TCP_MD5SIG:
 	case TCP_MD5SIG_EXT:

net/ipv4/tcp_ao.c

···
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * INET		An implementation of the TCP Authentication Option (TCP-AO).
+ *		See RFC5925.
+ *
+ * Authors:	Dmitry Safonov <[e-mail]>
+ *		Francesco Ruggeri <[e-mail]>
+ *		Salam Noureddine <[e-mail]>
+ */
+#define pr_fmt(fmt) "TCP: " fmt
+
+#include <crypto/hash.h>
+#include <linux/inetdevice.h>
+#include <linux/tcp.h>
+
+#include <net/tcp.h>
+#include <net/ipv6.h>
+
+/* Optimized version of tcp_ao_do_lookup(): only for sockets for which
+ * it's known that the keys in ao_info are matching peer's
+ * family/address/VRF/etc.
+ */
+static struct tcp_ao_key *tcp_ao_established_key(struct tcp_ao_info *ao,
+						 int sndid, int rcvid)
+{
+	struct tcp_ao_key *key;
+
+	hlist_for_each_entry_rcu(key, &ao->head, node) {
+		if ((sndid >= 0 && key->sndid != sndid) ||
+		    (rcvid >= 0 && key->rcvid != rcvid))
+			continue;
+		return key;
+	}
+
+	return NULL;
+}
+
+static int ipv4_prefix_cmp(const struct in_addr *addr1,
+			   const struct in_addr *addr2,
+			   unsigned int prefixlen)
+{
+	__be32 mask = inet_make_mask(prefixlen);
+	__be32 a1 = addr1->s_addr & mask;
+	__be32 a2 = addr2->s_addr & mask;
+
+	if (a1 == a2)
+		return 0;
+	return memcmp(&a1, &a2, sizeof(a1));
+}
+
+static int __tcp_ao_key_cmp(const struct tcp_ao_key *key,
+			    const union tcp_ao_addr *addr, u8 prefixlen,
+			    int family, int sndid, int rcvid)
+{
+	if (sndid >= 0 && key->sndid != sndid)
+		return (key->sndid > sndid) ? 1 : -1;
+	if (rcvid >= 0 && key->rcvid != rcvid)
+		return (key->rcvid > rcvid) ? 1 : -1;
+
+	if (family == AF_UNSPEC)
+		return 0;
+	if (key->family != family)
+		return (key->family > family) ? 1 : -1;
+
+	if (family == AF_INET) {
+		if (ntohl(key->addr.a4.s_addr) == INADDR_ANY)
+			return 0;
+		if (ntohl(addr->a4.s_addr) == INADDR_ANY)
+			return 0;
+		return ipv4_prefix_cmp(&key->addr.a4, &addr->a4, prefixlen);
+#if IS_ENABLED(CONFIG_IPV6)
+	} else {
+		if (ipv6_addr_any(&key->addr.a6) || ipv6_addr_any(&addr->a6))
+			return 0;
+		if (ipv6_prefix_equal(&key->addr.a6, &addr->a6, prefixlen))
+			return 0;
+		return memcmp(&key->addr.a6, &addr->a6, sizeof(addr->a6));
+#endif
+	}
+	return -1;
+}
+
+static int tcp_ao_key_cmp(const struct tcp_ao_key *key,
+			  const union tcp_ao_addr *addr, u8 prefixlen,
+			  int family, int sndid, int rcvid)
+{
+#if IS_ENABLED(CONFIG_IPV6)
+	if (family == AF_INET6 && ipv6_addr_v4mapped(&addr->a6)) {
+		__be32 addr4 = addr->a6.s6_addr32[3];
+
+		return __tcp_ao_key_cmp(key, (union tcp_ao_addr *)&addr4,
+					prefixlen, AF_INET, sndid, rcvid);
+	}
+#endif
+	return __tcp_ao_key_cmp(key, addr, prefixlen, family, sndid, rcvid);
+}
+
+static struct tcp_ao_key *__tcp_ao_do_lookup(const struct sock *sk,
+		const union tcp_ao_addr *addr, int family, u8 prefix,
+		int sndid, int rcvid)
+{
+	struct tcp_ao_key *key;
+	struct tcp_ao_info *ao;
+
+	ao = rcu_dereference_check(tcp_sk(sk)->ao_info,
+				   lockdep_sock_is_held(sk));
+	if (!ao)
+		return NULL;
+
+	hlist_for_each_entry_rcu(key, &ao->head, node) {
+		u8 prefixlen = min(prefix, key->prefixlen);
+
+		if (!tcp_ao_key_cmp(key, addr, prefixlen, family, sndid, rcvid))
+			return key;
+	}
+	return NULL;
+}
+
+static struct tcp_ao_info *tcp_ao_alloc_info(gfp_t flags)
+{
+	struct tcp_ao_info *ao;
+
+	ao = kzalloc(sizeof(*ao), flags);
+	if (!ao)
+		return NULL;
+	INIT_HLIST_HEAD(&ao->head);
+
+	return ao;
+}
+
+static void tcp_ao_link_mkt(struct tcp_ao_info *ao, struct tcp_ao_key *mkt)
+{
+	hlist_add_head_rcu(&mkt->node, &ao->head);
+}
+
+static void tcp_ao_key_free_rcu(struct rcu_head *head)
+{
+	struct tcp_ao_key *key = container_of(head, struct tcp_ao_key, rcu);
+
+	tcp_sigpool_release(key->tcp_sigpool_id);
+	kfree_sensitive(key);
+}
+
+void tcp_ao_destroy_sock(struct sock *sk)
+{
+	struct tcp_ao_info *ao;
+	struct tcp_ao_key *key;
+	struct hlist_node *n;
+
+	ao = rcu_dereference_protected(tcp_sk(sk)->ao_info, 1);
+	tcp_sk(sk)->ao_info = NULL;
+
+	if (!ao)
+		return;
+
+	hlist_for_each_entry_safe(key, n, &ao->head, node) {
+		hlist_del_rcu(&key->node);
+		atomic_sub(tcp_ao_sizeof_key(key), &sk->sk_omem_alloc);
+		call_rcu(&key->rcu, tcp_ao_key_free_rcu);
+	}
+
+	kfree_rcu(ao, rcu);
+}
+
+static bool tcp_ao_can_set_current_rnext(struct sock *sk)
+{
+	/* There aren't current/rnext keys on TCP_LISTEN sockets */
+	if (sk->sk_state == TCP_LISTEN)
+		return false;
+	return true;
+}
+
+static int tcp_ao_verify_ipv4(struct sock *sk, struct tcp_ao_add *cmd,
+			      union tcp_ao_addr **addr)
+{
+	struct sockaddr_in *sin = (struct sockaddr_in *)&cmd->addr;
+	struct inet_sock *inet = inet_sk(sk);
+
+	if (sin->sin_family != AF_INET)
+		return -EINVAL;
+
+	/* Currently matching is not performed on port (or port ranges) */
+	if (sin->sin_port != 0)
+		return -EINVAL;
+
+	/* Check prefix and trailing 0's in addr */
+	if (cmd->prefix != 0) {
+		__be32 mask;
+
+		if (ntohl(sin->sin_addr.s_addr) == INADDR_ANY)
+			return -EINVAL;
+		if (cmd->prefix > 32)
+			return -EINVAL;
+
+		mask = inet_make_mask(cmd->prefix);
+		if (sin->sin_addr.s_addr & ~mask)
+			return -EINVAL;
+
+		/* Check that MKT address is consistent with socket */
+		if (ntohl(inet->inet_daddr) != INADDR_ANY &&
+		    (inet->inet_daddr & mask) != sin->sin_addr.s_addr)
+			return -EINVAL;
+	} else {
+		if (ntohl(sin->sin_addr.s_addr) != INADDR_ANY)
+			return -EINVAL;
+	}
+
+	*addr = (union tcp_ao_addr *)&sin->sin_addr;
+	return 0;
+}
+
+static int tcp_ao_parse_crypto(struct tcp_ao_add *cmd, struct tcp_ao_key *key)
+{
+	unsigned int syn_tcp_option_space;
+	bool is_kdf_aes_128_cmac = false;
+	struct crypto_ahash *tfm;
+	struct tcp_sigpool hp;
+	void *tmp_key = NULL;
+	int err;
+
+	/* RFC5926, 3.1.1.2. KDF_AES_128_CMAC */
+	if (!strcmp("cmac(aes128)", cmd->alg_name)) {
+		strscpy(cmd->alg_name, "cmac(aes)", sizeof(cmd->alg_name));
+		is_kdf_aes_128_cmac = (cmd->keylen != 16);
+		tmp_key = kmalloc(cmd->keylen, GFP_KERNEL);
+		if (!tmp_key)
+			return -ENOMEM;
+	}
+
+	key->maclen = cmd->maclen ?: 12; /* 12 is the default in RFC5925 */
+
+	/* Check: maclen + tcp-ao header <= (MAX_TCP_OPTION_SPACE - mss
+	 *					- tstamp - wscale - sackperm),
+	 * see tcp_syn_options(), tcp_synack_options(), commit 33ad798c924b.
+	 *
+	 * In order to allow D-SACK with TCP-AO, the header size should be:
+	 * (MAX_TCP_OPTION_SPACE - TCPOLEN_TSTAMP_ALIGNED
+	 *			- TCPOLEN_SACK_BASE_ALIGNED
+	 *			- 2 * TCPOLEN_SACK_PERBLOCK) = 8 (maclen = 4),
+	 * see tcp_established_options().
+	 *
+	 * RFC5925, 2.2:
+	 * Typical MACs are 96-128 bits (12-16 bytes), but any length
+	 * that fits in the header of the segment being authenticated
+	 * is allowed.
+	 *
+	 * RFC5925, 7.6:
+	 * TCP-AO continues to consume 16 bytes in non-SYN segments,
+	 * leaving a total of 24 bytes for other options, of which
+	 * the timestamp consumes 10.  This leaves 14 bytes, of which 10
+	 * are used for a single SACK block. When two SACK blocks are used,
+	 * such as to handle D-SACK, a smaller TCP-AO MAC would be required
+	 * to make room for the additional SACK block (i.e., to leave 18
+	 * bytes for the D-SACK variant of the SACK option) [RFC2883].
+	 * Note that D-SACK is not supportable in TCP MD5 in the presence
+	 * of timestamps, because TCP MD5’s MAC length is fixed and too
+	 * large to leave sufficient option space.
+	 */
+	syn_tcp_option_space = MAX_TCP_OPTION_SPACE;
+	syn_tcp_option_space -= TCPOLEN_TSTAMP_ALIGNED;
+	syn_tcp_option_space -= TCPOLEN_WSCALE_ALIGNED;
+	syn_tcp_option_space -= TCPOLEN_SACKPERM_ALIGNED;
+	if (tcp_ao_len(key) > syn_tcp_option_space) {
+		err = -EMSGSIZE;
+		goto err_kfree;
+	}
+
+	key->keylen = cmd->keylen;
+	memcpy(key->key, cmd->key, cmd->keylen);
+
+	err = tcp_sigpool_start(key->tcp_sigpool_id, &hp);
+	if (err)
+		goto err_kfree;
+
+	tfm = crypto_ahash_reqtfm(hp.req);
+	if (is_kdf_aes_128_cmac) {
+		void *scratch = hp.scratch;
+		struct scatterlist sg;
+
+		memcpy(tmp_key, cmd->key, cmd->keylen);
+		sg_init_one(&sg, tmp_key, cmd->keylen);
+
+		/* Using zero-key of 16 bytes as described in RFC5926 */
+		memset(scratch, 0, 16);
+		err = crypto_ahash_setkey(tfm, scratch, 16);
+		if (err)
+			goto err_pool_end;
+
+		err = crypto_ahash_init(hp.req);
+		if (err)
+			goto err_pool_end;
+
+		ahash_request_set_crypt(hp.req, &sg, key->key, cmd->keylen);
+		err = crypto_ahash_update(hp.req);
+		if (err)
+			goto err_pool_end;
+
+		err |= crypto_ahash_final(hp.req);
+		if (err)
+			goto err_pool_end;
+		key->keylen = 16;
+	}
+
+	err = crypto_ahash_setkey(tfm, key->key, key->keylen);
+	if (err)
+		goto err_pool_end;
+
+	tcp_sigpool_end(&hp);
+	kfree_sensitive(tmp_key);
+
+	if (tcp_ao_maclen(key) > key->digest_size)
+		return -EINVAL;
+
+	return 0;
+
+err_pool_end:
+	tcp_sigpool_end(&hp);
+err_kfree:
+	kfree_sensitive(tmp_key);
+	return err;
+}
+
+#if IS_ENABLED(CONFIG_IPV6)
+static int tcp_ao_verify_ipv6(struct sock *sk, struct tcp_ao_add *cmd,
+			      union tcp_ao_addr **paddr,
+			      unsigned short int *family)
+{
+	struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *)&cmd->addr;
+	struct in6_addr *addr = &sin6->sin6_addr;
+	u8 prefix = cmd->prefix;
+
+	if (sin6->sin6_family != AF_INET6)
+		return -EINVAL;
+
+	/* Currently matching is not performed on port (or port ranges) */
+	if (sin6->sin6_port != 0)
+		return -EINVAL;
+
+	/* Check prefix and trailing 0's in addr */
+	if (cmd->prefix != 0 && ipv6_addr_v4mapped(addr)) {
+		__be32 addr4 = addr->s6_addr32[3];
+		__be32 mask;
+
+		if (prefix > 32 || ntohl(addr4) == INADDR_ANY)
+			return -EINVAL;
+
+		mask = inet_make_mask(prefix);
+		if (addr4 & ~mask)
+			return -EINVAL;
+
+		/* Check that MKT address is consistent with socket */
+		if (!ipv6_addr_any(&sk->sk_v6_daddr)) {
+			__be32 daddr4 = sk->sk_v6_daddr.s6_addr32[3];
+
+			if (!ipv6_addr_v4mapped(&sk->sk_v6_daddr))
+				return -EINVAL;
+			if ((daddr4 & mask) != addr4)
+				return -EINVAL;
+		}
+
+		*paddr = (union tcp_ao_addr *)&addr->s6_addr32[3];
+		*family = AF_INET;
+		return 0;
+	} else if (cmd->prefix != 0) {
+		struct in6_addr pfx;
+
+		if (ipv6_addr_any(addr) || prefix > 128)
+			return -EINVAL;
+
+		ipv6_addr_prefix(&pfx, addr, prefix);
+		if (ipv6_addr_cmp(&pfx, addr))
+			return -EINVAL;
+
+		/* Check that MKT address is consistent with socket */
+		if (!ipv6_addr_any(&sk->sk_v6_daddr) &&
+		    !ipv6_prefix_equal(&sk->sk_v6_daddr, addr, prefix))
+
+			return -EINVAL;
+	} else {
+		if (!ipv6_addr_any(addr))
+			return -EINVAL;
+	}
+
+	*paddr = (union tcp_ao_addr *)addr;
+	return 0;
+}
+#else
+static int tcp_ao_verify_ipv6(struct sock *sk, struct tcp_ao_add *cmd,
+			      union tcp_ao_addr **paddr,
+			      unsigned short int *family)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+
+static struct tcp_ao_info *setsockopt_ao_info(struct sock *sk)
+{
+	if (sk_fullsock(sk)) {
+		return rcu_dereference_protected(tcp_sk(sk)->ao_info,
+						 lockdep_sock_is_held(sk));
+	}
+	return ERR_PTR(-ESOCKTNOSUPPORT);
+}
+
+#define TCP_AO_KEYF_ALL		(0)
+
+static struct tcp_ao_key *tcp_ao_key_alloc(struct sock *sk,
+					   struct tcp_ao_add *cmd)
+{
+	const char *algo = cmd->alg_name;
+	unsigned int digest_size;
+	struct crypto_ahash *tfm;
+	struct tcp_ao_key *key;
+	struct tcp_sigpool hp;
+	int err, pool_id;
+	size_t size;
+
+	/* Force null-termination of alg_name */
+	cmd->alg_name[ARRAY_SIZE(cmd->alg_name) - 1] = '\0';
+
+	/* RFC5926, 3.1.1.2. KDF_AES_128_CMAC */
+	if (!strcmp("cmac(aes128)", algo))
+		algo = "cmac(aes)";
+
+	/* Full TCP header (th->doff << 2) should fit into scratch area,
+	 * see tcp_ao_hash_header().
+	 */
+	pool_id = tcp_sigpool_alloc_ahash(algo, 60);
+	if (pool_id < 0)
+		return ERR_PTR(pool_id);
+
+	err = tcp_sigpool_start(pool_id, &hp);
+	if (err)
+		goto err_free_pool;
+
+	tfm = crypto_ahash_reqtfm(hp.req);
+	if (crypto_ahash_alignmask(tfm) > TCP_AO_KEY_ALIGN) {
+		err = -EOPNOTSUPP;
+		goto err_pool_end;
+	}
+	digest_size = crypto_ahash_digestsize(tfm);
+	tcp_sigpool_end(&hp);
+
+	size = sizeof(struct tcp_ao_key) + (digest_size << 1);
+	key = sock_kmalloc(sk, size, GFP_KERNEL);
+	if (!key) {
+		err = -ENOMEM;
+		goto err_free_pool;
+	}
+
+	key->tcp_sigpool_id = pool_id;
+	key->digest_size = digest_size;
+	return key;
+
+err_pool_end:
+	tcp_sigpool_end(&hp);
+err_free_pool:
+	tcp_sigpool_release(pool_id);
+	return ERR_PTR(err);
+}
+
+static int tcp_ao_add_cmd(struct sock *sk, unsigned short int family,
+			  sockptr_t optval, int optlen)
+{
+	struct tcp_ao_info *ao_info;
+	union tcp_ao_addr *addr;
+	struct tcp_ao_key *key;
+	struct tcp_ao_add cmd;
+	bool first = false;
+	int ret;
+
+	if (optlen < sizeof(cmd))
+		return -EINVAL;
+
+	ret = copy_struct_from_sockptr(&cmd, sizeof(cmd), optval, optlen);
+	if (ret)
+		return ret;
+
+	if (cmd.keylen > TCP_AO_MAXKEYLEN)
+		return -EINVAL;
+
+	if (cmd.reserved != 0 || cmd.reserved2 != 0)
+		return -EINVAL;
+
+	if (family == AF_INET)
+		ret = tcp_ao_verify_ipv4(sk, &cmd, &addr);
+	else
+		ret = tcp_ao_verify_ipv6(sk, &cmd, &addr, &family);
+	if (ret)
+		return ret;
+
+	if (cmd.keyflags & ~TCP_AO_KEYF_ALL)
+		return -EINVAL;
+
+	if (cmd.set_current || cmd.set_rnext) {
+		if (!tcp_ao_can_set_current_rnext(sk))
+			return -EINVAL;
+	}
+
+	ao_info = setsockopt_ao_info(sk);
+	if (IS_ERR(ao_info))
+		return PTR_ERR(ao_info);
+
+	if (!ao_info) {
+		ao_info = tcp_ao_alloc_info(GFP_KERNEL);
+		if (!ao_info)
+			return -ENOMEM;
+		first = true;
+	} else {
+		/* Check that neither RecvID nor SendID match any
+		 * existing key for the peer, RFC5925 3.1:
+		 * > The IDs of MKTs MUST NOT overlap where their
+		 * > TCP connection identifiers overlap.
+		 */
+		if (__tcp_ao_do_lookup(sk, addr, family,
+				       cmd.prefix, -1, cmd.rcvid))
+			return -EEXIST;
+		if (__tcp_ao_do_lookup(sk, addr, family,
+				       cmd.prefix, cmd.sndid, -1))
+			return -EEXIST;
+	}
+
+	key = tcp_ao_key_alloc(sk, &cmd);
+	if (IS_ERR(key)) {
+		ret = PTR_ERR(key);
+		goto err_free_ao;
+	}
+
+	INIT_HLIST_NODE(&key->node);
+	memcpy(&key->addr, addr, (family == AF_INET) ? sizeof(struct in_addr) :
+						       sizeof(struct in6_addr));
+	key->prefixlen	= cmd.prefix;
+	key->family	= family;
+	key->keyflags	= cmd.keyflags;
+	key->sndid	= cmd.sndid;
+	key->rcvid	= cmd.rcvid;
+
+	ret = tcp_ao_parse_crypto(&cmd, key);
+	if (ret < 0)
+		goto err_free_sock;
+
+	tcp_ao_link_mkt(ao_info, key);
+	if (first) {
+		sk_gso_disable(sk);
+		rcu_assign_pointer(tcp_sk(sk)->ao_info, ao_info);
+	}
+
+	if (cmd.set_current)
+		WRITE_ONCE(ao_info->current_key, key);
+	if (cmd.set_rnext)
+		WRITE_ONCE(ao_info->rnext_key, key);
+	return 0;
+
+err_free_sock:
+	atomic_sub(tcp_ao_sizeof_key(key), &sk->sk_omem_alloc);
+	tcp_sigpool_release(key->tcp_sigpool_id);
+	kfree_sensitive(key);
+err_free_ao:
+	if (first)
+		kfree(ao_info);
+	return ret;
+}
+
+static int tcp_ao_delete_key(struct sock *sk, struct tcp_ao_info *ao_info,
+			     struct tcp_ao_key *key,
+			     struct tcp_ao_key *new_current,
+			     struct tcp_ao_key *new_rnext)
+{
+	int err;
+
+	hlist_del_rcu(&key->node);
+
+	/* At this moment another CPU could have looked this key up
+	 * while it was unlinked from the list. Wait for RCU grace period,
+	 * after which the key is off-list and can't be looked up again;
+	 * the rx path [just before RCU came] might have used it and set it
+	 * as current_key (very unlikely).
+	 */
+	synchronize_rcu();
+	if (new_current)
+		WRITE_ONCE(ao_info->current_key, new_current);
+	if (new_rnext)
+		WRITE_ONCE(ao_info->rnext_key, new_rnext);
+
+	if (unlikely(READ_ONCE(ao_info->current_key) == key ||
+		     READ_ONCE(ao_info->rnext_key) == key)) {
+		err = -EBUSY;
+		goto add_key;
+	}
+
+	atomic_sub(tcp_ao_sizeof_key(key), &sk->sk_omem_alloc);
+	call_rcu(&key->rcu, tcp_ao_key_free_rcu);
+
+	return 0;
+add_key:
+	hlist_add_head_rcu(&key->node, &ao_info->head);
+	return err;
+}
+
+static int tcp_ao_del_cmd(struct sock *sk, unsigned short int family,
+			  sockptr_t optval, int optlen)
+{
+	struct tcp_ao_key *key, *new_current = NULL, *new_rnext = NULL;
+	struct tcp_ao_info *ao_info;
+	union tcp_ao_addr *addr;
+	struct tcp_ao_del cmd;
+	int addr_len;
+	__u8 prefix;
+	u16 port;
+	int err;
+
+	if (optlen < sizeof(cmd))
+		return -EINVAL;
+
+	err = copy_struct_from_sockptr(&cmd, sizeof(cmd), optval, optlen);
+	if (err)
+		return err;
+
+	if (cmd.reserved != 0 || cmd.reserved2 != 0)
+		return -EINVAL;
+
+	if (cmd.set_current || cmd.set_rnext) {
+		if (!tcp_ao_can_set_current_rnext(sk))
+			return -EINVAL;
+	}
+
+	ao_info = setsockopt_ao_info(sk);
+	if (IS_ERR(ao_info))
+		return PTR_ERR(ao_info);
+	if (!ao_info)
+		return -ENOENT;
+
+	/* For sockets in TCP_CLOSED it's possible set keys that aren't
+	 * matching the future peer (address/VRF/etc),
+	 * tcp_ao_connect_init() will choose a correct matching MKT
+	 * if there's any.
+	 */
+	if (cmd.set_current) {
+		new_current = tcp_ao_established_key(ao_info, cmd.current_key, -1);
+		if (!new_current)
+			return -ENOENT;
+	}
+	if (cmd.set_rnext) {
+		new_rnext = tcp_ao_established_key(ao_info, -1, cmd.rnext);
+		if (!new_rnext)
+			return -ENOENT;
+	}
+
+	if (family == AF_INET) {
+		struct sockaddr_in *sin = (struct sockaddr_in *)&cmd.addr;
+
+		addr = (union tcp_ao_addr *)&sin->sin_addr;
+		addr_len = sizeof(struct in_addr);
+		port = ntohs(sin->sin_port);
+	} else {
+		struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *)&cmd.addr;
+		struct in6_addr *addr6 = &sin6->sin6_addr;
+
+		if (ipv6_addr_v4mapped(addr6)) {
+			addr = (union tcp_ao_addr *)&addr6->s6_addr32[3];
+			addr_len = sizeof(struct in_addr);
+			family = AF_INET;
+		} else {
+			addr = (union tcp_ao_addr *)addr6;
+			addr_len = sizeof(struct in6_addr);
+		}
+		port = ntohs(sin6->sin6_port);
+	}
+	prefix = cmd.prefix;
+
+	/* Currently matching is not performed on port (or port ranges) */
+	if (port != 0)
+		return -EINVAL;
+
+	/* We could choose random present key here for current/rnext
+	 * but that's less predictable. Let's be strict and don't
+	 * allow removing a key that's in use. RFC5925 doesn't
+	 * specify how-to coordinate key removal, but says:
+	 * "It is presumed that an MKT affecting a particular
+	 * connection cannot be destroyed during an active connection"
+	 */
+	hlist_for_each_entry_rcu(key, &ao_info->head, node) {
+		if (cmd.sndid != key->sndid ||
+		    cmd.rcvid != key->rcvid)
+			continue;
+
+		if (family != key->family ||
+		    prefix != key->prefixlen ||
+		    memcmp(addr, &key->addr, addr_len))
+			continue;
+
+		if (key == new_current || key == new_rnext)
+			continue;
+
+		return tcp_ao_delete_key(sk, ao_info, key,
+					  new_current, new_rnext);
+	}
+	return -ENOENT;
+}
+
+static int tcp_ao_info_cmd(struct sock *sk, unsigned short int family,
+			   sockptr_t optval, int optlen)
+{
+	struct tcp_ao_key *new_current = NULL, *new_rnext = NULL;
+	struct tcp_ao_info *ao_info;
+	struct tcp_ao_info_opt cmd;
+	bool first = false;
+	int err;
+
+	if (optlen < sizeof(cmd))
+		return -EINVAL;
+
+	err = copy_struct_from_sockptr(&cmd, sizeof(cmd), optval, optlen);
+	if (err)
+		return err;
+
+	if (cmd.set_current || cmd.set_rnext) {
+		if (!tcp_ao_can_set_current_rnext(sk))
+			return -EINVAL;
+	}
+
+	if (cmd.reserved != 0)
+		return -EINVAL;
+
+	ao_info = setsockopt_ao_info(sk);
+	if (IS_ERR(ao_info))
+		return PTR_ERR(ao_info);
+	if (!ao_info) {
+		ao_info = tcp_ao_alloc_info(GFP_KERNEL);
+		if (!ao_info)
+			return -ENOMEM;
+		first = true;
+	}
+
+	/* For sockets in TCP_CLOSED it's possible set keys that aren't
+	 * matching the future peer (address/port/VRF/etc),
+	 * tcp_ao_connect_init() will choose a correct matching MKT
+	 * if there's any.
+	 */
+	if (cmd.set_current) {
+		new_current = tcp_ao_established_key(ao_info, cmd.current_key, -1);
+		if (!new_current) {
+			err = -ENOENT;
+			goto out;
+		}
+	}
+	if (cmd.set_rnext) {
+		new_rnext = tcp_ao_established_key(ao_info, -1, cmd.rnext);
+		if (!new_rnext) {
+			err = -ENOENT;
+			goto out;
+		}
+	}
+
+	ao_info->ao_required = cmd.ao_required;
+	if (new_current)
+		WRITE_ONCE(ao_info->current_key, new_current);
+	if (new_rnext)
+		WRITE_ONCE(ao_info->rnext_key, new_rnext);
+	if (first) {
+		sk_gso_disable(sk);
+		rcu_assign_pointer(tcp_sk(sk)->ao_info, ao_info);
+	}
+	return 0;
+out:
+	if (first)
+		kfree(ao_info);
+	return err;
+}
+
+int tcp_parse_ao(struct sock *sk, int cmd, unsigned short int family,
+		 sockptr_t optval, int optlen)
+{
+	if (WARN_ON_ONCE(family != AF_INET && family != AF_INET6))
+		return -EAFNOSUPPORT;
+
+	switch (cmd) {
+	case TCP_AO_ADD_KEY:
+		return tcp_ao_add_cmd(sk, family, optval, optlen);
+	case TCP_AO_DEL_KEY:
+		return tcp_ao_del_cmd(sk, family, optval, optlen);
+	case TCP_AO_INFO:
+		return tcp_ao_info_cmd(sk, family, optval, optlen);
+	default:
+		WARN_ON_ONCE(1);
+		return -EINVAL;
+	}
+}
+
+int tcp_v4_parse_ao(struct sock *sk, int cmd, sockptr_t optval, int optlen)
+{
+	return tcp_parse_ao(sk, cmd, AF_INET, optval, optlen);
+}
+

net/ipv4/tcp_ipv4.c

···
 };
 EXPORT_SYMBOL(ipv4_specific);
 
-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
 static const struct tcp_sock_af_ops tcp_sock_ipv4_specific = {
+#ifdef CONFIG_TCP_MD5SIG
 	.md5_lookup		= tcp_v4_md5_lookup,
 	.calc_md5_hash		= tcp_v4_md5_hash_skb,
 	.md5_parse		= tcp_v4_parse_md5_keys,
+#endif
+#ifdef CONFIG_TCP_AO
+	.ao_parse		= tcp_v4_parse_ao,
+#endif
 };
 #endif
 
···
 
 	icsk->icsk_af_ops = &ipv4_specific;
 
-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
 	tcp_sk(sk)->af_specific = &tcp_sock_ipv4_specific;
 #endif
 
···
 		rcu_assign_pointer(tp->md5sig_info, NULL);
 	}
 #endif
+	tcp_ao_destroy_sock(sk);
 
 	/* Clean up a referenced TCP bind bucket. */
 	if (inet_csk(sk)->icsk_bind_hash)

net/ipv6/Makefile

···
 ifneq ($(CONFIG_IPV6),)
 obj-$(CONFIG_NET_UDP_TUNNEL) += ip6_udp_tunnel.o
 obj-y += mcast_snoop.o
+obj-$(CONFIG_TCP_AO) += tcp_ao.o
 endif

net/ipv6/tcp_ao.c

···
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * INET		An implementation of the TCP Authentication Option (TCP-AO).
+ *		See RFC5925.
+ *
+ * Authors:	Dmitry Safonov <[e-mail]>
+ *		Francesco Ruggeri <[e-mail]>
+ *		Salam Noureddine <[e-mail]>
+ */
+#include <linux/tcp.h>
+
+#include <net/tcp.h>
+#include <net/ipv6.h>
+
+int tcp_v6_parse_ao(struct sock *sk, int cmd,
+		    sockptr_t optval, int optlen)
+{
+	return tcp_parse_ao(sk, cmd, AF_INET6, optval, optlen);
+}

net/ipv6/tcp_ipv6.c

···
 
 static const struct inet_connection_sock_af_ops ipv6_mapped;
 const struct inet_connection_sock_af_ops ipv6_specific;
-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
 static const struct tcp_sock_af_ops tcp_sock_ipv6_specific;
 static const struct tcp_sock_af_ops tcp_sock_ipv6_mapped_specific;
-#else
-static struct tcp_md5sig_key *tcp_v6_md5_do_lookup(const struct sock *sk,
-						   const struct in6_addr *addr,
-						   int l3index)
-{
-	return NULL;
-}
 #endif
 
 /* Helper returning the inet6 address from a given tcp socket.
···
 		if (sk_is_mptcp(sk))
 			mptcpv6_handle_mapped(sk, true);
 		sk->sk_backlog_rcv = tcp_v4_do_rcv;
-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
 		tp->af_specific = &tcp_sock_ipv6_mapped_specific;
 #endif
 
···
 			if (sk_is_mptcp(sk))
 				mptcpv6_handle_mapped(sk, false);
 			sk->sk_backlog_rcv = tcp_v6_do_rcv;
-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
 			tp->af_specific = &tcp_sock_ipv6_specific;
 #endif
 			goto failure;
···
 	memset(md5_hash, 0, 16);
 	return 1;
 }
-
+#else /* CONFIG_TCP_MD5SIG */
+static struct tcp_md5sig_key *tcp_v6_md5_do_lookup(const struct sock *sk,
+						   const struct in6_addr *addr,
+						   int l3index)
+{
+	return NULL;
+}
 #endif
 
 static void tcp_v6_init_req(struct request_sock *req,
···
 		if (sk_is_mptcp(newsk))
 			mptcpv6_handle_mapped(newsk, true);
 		newsk->sk_backlog_rcv = tcp_v4_do_rcv;
-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
 		newtp->af_specific = &tcp_sock_ipv6_mapped_specific;
 #endif
 
···
 	.mtu_reduced	   = tcp_v6_mtu_reduced,
 };
 
-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
 static const struct tcp_sock_af_ops tcp_sock_ipv6_specific = {
+#ifdef CONFIG_TCP_MD5SIG
 	.md5_lookup	=	tcp_v6_md5_lookup,
 	.calc_md5_hash	=	tcp_v6_md5_hash_skb,
 	.md5_parse	=	tcp_v6_parse_md5_keys,
+#endif
+#ifdef CONFIG_TCP_AO
+	.ao_parse	=	tcp_v6_parse_ao,
+#endif
 };
 #endif
 
···
 	.mtu_reduced	   = tcp_v4_mtu_reduced,
 };
 
-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
 static const struct tcp_sock_af_ops tcp_sock_ipv6_mapped_specific = {
+#ifdef CONFIG_TCP_MD5SIG
 	.md5_lookup	=	tcp_v4_md5_lookup,
 	.calc_md5_hash	=	tcp_v4_md5_hash_skb,
 	.md5_parse	=	tcp_v6_parse_md5_keys,
+#endif
+#ifdef CONFIG_TCP_AO
+	.ao_parse	=	tcp_v6_parse_ao,
+#endif
 };
 #endif
 
···
 
 	icsk->icsk_af_ops = &ipv6_specific;
 
-#ifdef CONFIG_TCP_MD5SIG
+#if defined(CONFIG_TCP_MD5SIG) || defined(CONFIG_TCP_AO)
 	tcp_sk(sk)->af_specific = &tcp_sock_ipv6_specific;
 #endif