upstream: Record session ID, host key and sig at intital KEX

These will be used later for agent session ID / hostkey binding

ok markus@

OpenBSD-Commit-ID: a9af29e33772b18e3e867c6fa8ab35e1694a81fe

5 files changed, 69 insertions, 13 deletions

diff --git a/kex.c b/kex.c
index 709a0ec63..55babbcec 100644
--- a/kex.c
+++ b/kex.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kex.c,v 1.168 2021/04/03 06:18:40 djm Exp $ */
+/* $OpenBSD: kex.c,v 1.169 2021/12/19 22:08:06 djm Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  *
@@ -699,6 +699,8 @@ kex_free(struct kex *kex)
 	sshbuf_free(kex->server_version);
 	sshbuf_free(kex->client_pub);
 	sshbuf_free(kex->session_id);
+	sshbuf_free(kex->initial_sig);
+	sshkey_free(kex->initial_hostkey);
 	free(kex->failed_choice);
 	free(kex->hostkey_alg);
 	free(kex->name);
diff --git a/kex.h b/kex.h
index 9605ed528..70b8909bc 100644
--- a/kex.h
+++ b/kex.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: kex.h,v 1.114 2021/01/31 22:55:29 djm Exp $ */
+/* $OpenBSD: kex.h,v 1.115 2021/12/19 22:08:06 djm Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -130,6 +130,7 @@ struct newkeys {
 };
 
 struct ssh;
+struct sshbuf;
 
 struct kex {
 	struct newkeys	*newkeys[MODE_MAX];
@@ -148,6 +149,8 @@ struct kex {
 	struct sshbuf *client_version;
 	struct sshbuf *server_version;
 	struct sshbuf *session_id;
+	struct sshbuf *initial_sig;
+	struct sshkey *initial_hostkey;
 	sig_atomic_t done;
 	u_int	flags;
 	int	hash_alg;
diff --git a/kexgen.c b/kexgen.c
index bde28053d..20f3c5711 100644
--- a/kexgen.c
+++ b/kexgen.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kexgen.c,v 1.7 2021/04/03 06:18:40 djm Exp $ */
+/* $OpenBSD: kexgen.c,v 1.8 2021/12/19 22:08:06 djm Exp $ */
 /*
  * Copyright (c) 2019 Markus Friedl.  All rights reserved.
  *
@@ -218,8 +218,26 @@ input_kex_gen_reply(int type, u_int32_t seq, struct ssh *ssh)
 	    kex->hostkey_alg, ssh->compat, NULL)) != 0)
 		goto out;
 
-	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
-		r = kex_send_newkeys(ssh);
+	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
+	    (r = kex_send_newkeys(ssh)) != 0)
+		goto out;
+
+	/* save initial signature and hostkey */
+	if ((kex->flags & KEX_INITIAL) != 0) {
+		if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) {
+			r = SSH_ERR_INTERNAL_ERROR;
+			goto out;
+		}
+		if ((kex->initial_sig = sshbuf_new()) == NULL) {
+			r = SSH_ERR_ALLOC_FAIL;
+			goto out;
+		}
+		if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0)
+			goto out;
+		kex->initial_hostkey = server_host_key;
+		server_host_key = NULL;
+	}
+	/* success */
 out:
 	explicit_bzero(hash, sizeof(hash));
 	explicit_bzero(kex->c25519_client_key, sizeof(kex->c25519_client_key));
@@ -333,8 +351,15 @@ input_kex_gen_init(int type, u_int32_t seq, struct ssh *ssh)
 	    (r = sshpkt_send(ssh)) != 0)
 		goto out;
 
-	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
-		r = kex_send_newkeys(ssh);
+	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
+	    (r = kex_send_newkeys(ssh)) != 0)
+		goto out;
+	/* retain copy of hostkey used at initial KEX */
+	if (kex->initial_hostkey == NULL &&
+	    (r = sshkey_from_private(server_host_public,
+	    &kex->initial_hostkey)) != 0)
+		goto out;
+	/* success */
 out:
 	explicit_bzero(hash, sizeof(hash));
 	sshbuf_free(server_host_key_blob);
diff --git a/kexgexc.c b/kexgexc.c
index 4a2e741d8..e99e0cf21 100644
--- a/kexgexc.c
+++ b/kexgexc.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kexgexc.c,v 1.37 2021/01/31 22:55:29 djm Exp $ */
+/* $OpenBSD: kexgexc.c,v 1.38 2021/12/19 22:08:06 djm Exp $ */
 /*
  * Copyright (c) 2000 Niels Provos.  All rights reserved.
  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
@@ -206,8 +206,26 @@ input_kex_dh_gex_reply(int type, u_int32_t seq, struct ssh *ssh)
 	    hashlen, kex->hostkey_alg, ssh->compat, NULL)) != 0)
 		goto out;
 
-	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
-		r = kex_send_newkeys(ssh);
+	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
+	    (r = kex_send_newkeys(ssh)) != 0)
+		goto out;
+
+	/* save initial signature and hostkey */
+	if ((kex->flags & KEX_INITIAL) != 0) {
+		if (kex->initial_hostkey != NULL || kex->initial_sig != NULL) {
+			r = SSH_ERR_INTERNAL_ERROR;
+			goto out;
+		}
+		if ((kex->initial_sig = sshbuf_new()) == NULL) {
+			r = SSH_ERR_ALLOC_FAIL;
+			goto out;
+		}
+		if ((r = sshbuf_put(kex->initial_sig, signature, slen)) != 0)
+			goto out;
+		kex->initial_hostkey = server_host_key;
+		server_host_key = NULL;
+	}
+	/* success */
  out:
 	explicit_bzero(hash, sizeof(hash));
 	DH_free(kex->dh);
diff --git a/kexgexs.c b/kexgexs.c
index f0fbcb912..72b444f69 100644
--- a/kexgexs.c
+++ b/kexgexs.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kexgexs.c,v 1.43 2021/01/31 22:55:29 djm Exp $ */
+/* $OpenBSD: kexgexs.c,v 1.44 2021/12/19 22:08:06 djm Exp $ */
 /*
  * Copyright (c) 2000 Niels Provos.  All rights reserved.
  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
@@ -194,8 +194,16 @@ input_kex_dh_gex_init(int type, u_int32_t seq, struct ssh *ssh)
 	    (r = sshpkt_send(ssh)) != 0)
 		goto out;
 
-	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) == 0)
-		r = kex_send_newkeys(ssh);
+	if ((r = kex_derive_keys(ssh, hash, hashlen, shared_secret)) != 0 ||
+	    (r = kex_send_newkeys(ssh)) != 0)
+		goto out;
+
+	/* retain copy of hostkey used at initial KEX */
+	if (kex->initial_hostkey == NULL &&
+	    (r = sshkey_from_private(server_host_public,
+	    &kex->initial_hostkey)) != 0)
+		goto out;
+	/* success */
  out:
 	explicit_bzero(hash, sizeof(hash));
 	DH_free(kex->dh);