net/tcp: Prevent TCP-MD5 with TCP-AO being set

Be as conservative as possible: if there is TCP-MD5 key for a given peer
regardless of L3 interface - don't allow setting TCP-AO key for the same
peer. According to RFC5925, TCP-AO is supposed to replace TCP-MD5 and
there can't be any switch between both on any connected tuple.
Later it can be relaxed, if there's a use, but in the beginning restrict
any intersection.

Note: it's still should be possible to set both TCP-MD5 and TCP-AO keys
on a listening socket for *different* peers.

Co-developed-by: Francesco Ruggeri <fruggeri@arista.com>
Signed-off-by: Francesco Ruggeri <fruggeri@arista.com>
Co-developed-by: Salam Noureddine <noureddine@arista.com>
Signed-off-by: Salam Noureddine <noureddine@arista.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Acked-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 105 insertions, 3 deletions

diff --git a/net/ipv4/tcp_ao.c b/net/ipv4/tcp_ao.c
index 3c2d005a37ce..ee23356101f4 100644
--- a/net/ipv4/tcp_ao.c
+++ b/net/ipv4/tcp_ao.c
@@ -116,6 +116,13 @@ static struct tcp_ao_key *__tcp_ao_do_lookup(const struct sock *sk,
 	return NULL;
 }
 
+struct tcp_ao_key *tcp_ao_do_lookup(const struct sock *sk,
+				    const union tcp_ao_addr *addr,
+				    int family, int sndid, int rcvid)
+{
+	return __tcp_ao_do_lookup(sk, addr, family, U8_MAX, sndid, rcvid);
+}
+
 static struct tcp_ao_info *tcp_ao_alloc_info(gfp_t flags)
 {
 	struct tcp_ao_info *ao;
@@ -162,6 +169,14 @@ void tcp_ao_destroy_sock(struct sock *sk)
 	kfree_rcu(ao, rcu);
 }
 
+struct tcp_ao_key *tcp_v4_ao_lookup(const struct sock *sk, struct sock *addr_sk,
+				    int sndid, int rcvid)
+{
+	union tcp_ao_addr *addr = (union tcp_ao_addr *)&addr_sk->sk_daddr;
+
+	return tcp_ao_do_lookup(sk, addr, AF_INET, sndid, rcvid);
+}
+
 static bool tcp_ao_can_set_current_rnext(struct sock *sk)
 {
 	/* There aren't current/rnext keys on TCP_LISTEN sockets */
@@ -497,6 +512,10 @@ static int tcp_ao_add_cmd(struct sock *sk, unsigned short int family,
 			return -EINVAL;
 	}
 
+	/* Don't allow keys for peers that have a matching TCP-MD5 key */
+	if (tcp_md5_do_lookup_any_l3index(sk, addr, family))
+		return -EKEYREJECTED;
+
 	ao_info = setsockopt_ao_info(sk);
 	if (IS_ERR(ao_info))
 		return PTR_ERR(ao_info);
@@ -698,6 +717,31 @@ static int tcp_ao_del_cmd(struct sock *sk, unsigned short int family,
 	return -ENOENT;
 }
 
+/* cmd.ao_required makes a socket TCP-AO only.
+ * Don't allow any md5 keys for any l3intf on the socket together with it.
+ * Restricting it early in setsockopt() removes a check for
+ * ao_info->ao_required on inbound tcp segment fast-path.
+ */
+static int tcp_ao_required_verify(struct sock *sk)
+{
+#ifdef CONFIG_TCP_MD5SIG
+	const struct tcp_md5sig_info *md5sig;
+
+	if (!static_branch_unlikely(&tcp_md5_needed.key))
+		return 0;
+
+	md5sig = rcu_dereference_check(tcp_sk(sk)->md5sig_info,
+				       lockdep_sock_is_held(sk));
+	if (!md5sig)
+		return 0;
+
+	if (rcu_dereference_check(hlist_first_rcu(&md5sig->head),
+				  lockdep_sock_is_held(sk)))
+		return 1;
+#endif
+	return 0;
+}
+
 static int tcp_ao_info_cmd(struct sock *sk, unsigned short int family,
 			   sockptr_t optval, int optlen)
 {
@@ -732,6 +776,9 @@ static int tcp_ao_info_cmd(struct sock *sk, unsigned short int family,
 		first = true;
 	}
 
+	if (cmd.ao_required && tcp_ao_required_verify(sk))
+		return -EKEYREJECTED;
+
 	/* 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
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index a4746c27f38a..698e58a3ccec 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1082,7 +1082,7 @@ static bool better_md5_match(struct tcp_md5sig_key *old, struct tcp_md5sig_key *
 /* Find the Key structure for an address.  */
 struct tcp_md5sig_key *__tcp_md5_do_lookup(const struct sock *sk, int l3index,
 					   const union tcp_md5_addr *addr,
-					   int family)
+					   int family, bool any_l3index)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	struct tcp_md5sig_key *key;
@@ -1101,7 +1101,8 @@ struct tcp_md5sig_key *__tcp_md5_do_lookup(const struct sock *sk, int l3index,
 				 lockdep_sock_is_held(sk)) {
 		if (key->family != family)
 			continue;
-		if (key->flags & TCP_MD5SIG_FLAG_IFINDEX && key->l3index != l3index)
+		if (!any_l3index && key->flags & TCP_MD5SIG_FLAG_IFINDEX &&
+		    key->l3index != l3index)
 			continue;
 		if (family == AF_INET) {
 			mask = inet_make_mask(key->prefixlen);
@@ -1313,7 +1314,7 @@ int tcp_md5_do_del(struct sock *sk, const union tcp_md5_addr *addr, int family,
 }
 EXPORT_SYMBOL(tcp_md5_do_del);
 
-static void tcp_clear_md5_list(struct sock *sk)
+void tcp_clear_md5_list(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct tcp_md5sig_key *key;
@@ -1383,6 +1384,12 @@ static int tcp_v4_parse_md5_keys(struct sock *sk, int optname,
 	if (cmd.tcpm_keylen > TCP_MD5SIG_MAXKEYLEN)
 		return -EINVAL;
 
+	/* Don't allow keys for peers that have a matching TCP-AO key.
+	 * See the comment in tcp_ao_add_cmd()
+	 */
+	if (tcp_ao_required(sk, addr, AF_INET))
+		return -EKEYREJECTED;
+
 	return tcp_md5_do_add(sk, addr, AF_INET, prefixlen, l3index, flags,
 			      cmd.tcpm_key, cmd.tcpm_keylen);
 }
@@ -2279,6 +2286,7 @@ static const struct tcp_sock_af_ops tcp_sock_ipv4_specific = {
 	.md5_parse		= tcp_v4_parse_md5_keys,
 #endif
 #ifdef CONFIG_TCP_AO
+	.ao_lookup		= tcp_v4_ao_lookup,
 	.ao_parse		= tcp_v4_parse_ao,
 #endif
 };
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index ca4d7594efd4..1b90107f7038 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3931,6 +3931,53 @@ int tcp_connect(struct sock *sk)
 
 	tcp_call_bpf(sk, BPF_SOCK_OPS_TCP_CONNECT_CB, 0, NULL);
 
+#if defined(CONFIG_TCP_MD5SIG) && defined(CONFIG_TCP_AO)
+	/* Has to be checked late, after setting daddr/saddr/ops.
+	 * Return error if the peer has both a md5 and a tcp-ao key
+	 * configured as this is ambiguous.
+	 */
+	if (unlikely(rcu_dereference_protected(tp->md5sig_info,
+					       lockdep_sock_is_held(sk)))) {
+		bool needs_ao = !!tp->af_specific->ao_lookup(sk, sk, -1, -1);
+		bool needs_md5 = !!tp->af_specific->md5_lookup(sk, sk);
+		struct tcp_ao_info *ao_info;
+
+		ao_info = rcu_dereference_check(tp->ao_info,
+						lockdep_sock_is_held(sk));
+		if (ao_info) {
+			/* This is an extra check: tcp_ao_required() in
+			 * tcp_v{4,6}_parse_md5_keys() should prevent adding
+			 * md5 keys on ao_required socket.
+			 */
+			needs_ao |= ao_info->ao_required;
+			WARN_ON_ONCE(ao_info->ao_required && needs_md5);
+		}
+		if (needs_md5 && needs_ao)
+			return -EKEYREJECTED;
+
+		/* If we have a matching md5 key and no matching tcp-ao key
+		 * then free up ao_info if allocated.
+		 */
+		if (needs_md5) {
+			tcp_ao_destroy_sock(sk);
+		} else if (needs_ao) {
+			tcp_clear_md5_list(sk);
+			kfree(rcu_replace_pointer(tp->md5sig_info, NULL,
+						  lockdep_sock_is_held(sk)));
+		}
+	}
+#endif
+#ifdef CONFIG_TCP_AO
+	if (unlikely(rcu_dereference_protected(tp->ao_info,
+					       lockdep_sock_is_held(sk)))) {
+		/* Don't allow connecting if ao is configured but no
+		 * matching key is found.
+		 */
+		if (!tp->af_specific->ao_lookup(sk, sk, -1, -1))
+			return -EKEYREJECTED;
+	}
+#endif
+
 	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
 		return -EHOSTUNREACH; /* Routing failure or similar. */