Refactor creation of KEX proposal.

This adds kex_proposal_populate_entries (and corresponding free) which
populates the KEX proposal array with dynamically allocated strings.
This replaces the previous mix of static and dynamic that has been the
source of previous leaks and bugs.  Remove unused compat functions.
With & ok djm@.

6 files changed, 102 insertions, 86 deletions

diff --git a/usr.bin/ssh/compat.c b/usr.bin/ssh/compat.c
index 38108fc8aa7..fba64bd4fc4 100644
--- a/usr.bin/ssh/compat.c
+++ b/usr.bin/ssh/compat.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: compat.c,v 1.125 2023/02/17 04:22:50 dtucker Exp $ */
+/* $OpenBSD: compat.c,v 1.126 2023/03/06 12:14:48 dtucker Exp $ */
 /*
  * Copyright (c) 1999, 2000, 2001, 2002 Markus Friedl.  All rights reserved.
  *
@@ -34,7 +34,6 @@
 #include "compat.h"
 #include "log.h"
 #include "match.h"
-#include "kex.h"
 
 /* determine bug flags from SSH protocol banner */
 void
@@ -138,21 +137,7 @@ compat_banner(struct ssh *ssh, const char *version)
 
 /* Always returns pointer to allocated memory, caller must free. */
 char *
-compat_cipher_proposal(struct ssh *ssh, char *cipher_prop)
-{
-	return xstrdup(cipher_prop);
-}
-
-/* Always returns pointer to allocated memory, caller must free. */
-char *
-compat_pkalg_proposal(struct ssh *ssh, char *pkalg_prop)
-{
-	return xstrdup(pkalg_prop);
-}
-
-/* Always returns pointer to allocated memory, caller must free. */
-char *
-compat_kex_proposal(struct ssh *ssh, char *p)
+compat_kex_proposal(struct ssh *ssh, const char *p)
 {
 	char *cp = NULL, *cp2 = NULL;
 
diff --git a/usr.bin/ssh/compat.h b/usr.bin/ssh/compat.h
index 1da367e84f7..1a19060fc14 100644
--- a/usr.bin/ssh/compat.h
+++ b/usr.bin/ssh/compat.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: compat.h,v 1.61 2023/02/17 04:22:50 dtucker Exp $ */
+/* $OpenBSD: compat.h,v 1.62 2023/03/06 12:14:48 dtucker Exp $ */
 
 /*
  * Copyright (c) 1999, 2000, 2001 Markus Friedl.  All rights reserved.
@@ -61,7 +61,5 @@
 struct ssh;
 
 void    compat_banner(struct ssh *, const char *);
-char	*compat_cipher_proposal(struct ssh *, char *);
-char	*compat_pkalg_proposal(struct ssh *, char *);
-char	*compat_kex_proposal(struct ssh *, char *);
+char	*compat_kex_proposal(struct ssh *, const char *);
 #endif
diff --git a/usr.bin/ssh/kex.c b/usr.bin/ssh/kex.c
index 7a0bd15912c..4997b024bb3 100644
--- a/usr.bin/ssh/kex.c
+++ b/usr.bin/ssh/kex.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kex.c,v 1.175 2023/02/28 21:31:50 dtucker Exp $ */
+/* $OpenBSD: kex.c,v 1.176 2023/03/06 12:14:48 dtucker Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  *
@@ -52,10 +52,12 @@
 #include "misc.h"
 #include "dispatch.h"
 #include "monitor.h"
+#include "myproposal.h"
 
 #include "ssherr.h"
 #include "sshbuf.h"
 #include "digest.h"
+#include "xmalloc.h"
 
 /* prototype */
 static int kex_choose_conf(struct ssh *);
@@ -302,6 +304,61 @@ kex_assemble_names(char **listp, const char *def, const char *all)
 	return r;
 }
 
+/*
+ * Fill out a proposal array with dynamically allocated values, which may
+ * be modified as required for compatibility reasons.
+ * Any of the options may be NULL, in which case the default is used.
+ * Array contents must be freed by calling kex_proposal_free_entries.
+ */
+void
+kex_proposal_populate_entries(struct ssh *ssh, char *prop[PROPOSAL_MAX],
+    const char *kexalgos, const char *ciphers, const char *macs,
+    const char *comp, const char *hkalgs)
+{
+	const char *defpropserver[PROPOSAL_MAX] = { KEX_SERVER };
+	const char *defpropclient[PROPOSAL_MAX] = { KEX_CLIENT };
+	const char **defprop = ssh->kex->server ? defpropserver : defpropclient;
+	u_int i;
+
+	if (prop == NULL)
+		fatal_f("proposal missing");
+
+	for (i = 0; i < PROPOSAL_MAX; i++) {
+		switch(i) {
+		case PROPOSAL_KEX_ALGS:
+			prop[i] = compat_kex_proposal(ssh,
+			    kexalgos ? kexalgos : defprop[i]);
+			break;
+		case PROPOSAL_ENC_ALGS_CTOS:
+		case PROPOSAL_ENC_ALGS_STOC:
+			prop[i] = xstrdup(ciphers ? ciphers : defprop[i]);
+			break;
+		case PROPOSAL_MAC_ALGS_CTOS:
+		case PROPOSAL_MAC_ALGS_STOC:
+			prop[i]  = xstrdup(macs ? macs : defprop[i]);
+			break;
+		case PROPOSAL_COMP_ALGS_CTOS:
+		case PROPOSAL_COMP_ALGS_STOC:
+			prop[i] = xstrdup(comp ? comp : defprop[i]);
+			break;
+		case PROPOSAL_SERVER_HOST_KEY_ALGS:
+			prop[i] = xstrdup(hkalgs ? hkalgs : defprop[i]);
+			break;
+		default:
+			prop[i] = xstrdup(defprop[i]);
+		}
+	}
+}
+
+void
+kex_proposal_free_entries(char *prop[PROPOSAL_MAX])
+{
+	u_int i;
+
+	for (i = 0; i < PROPOSAL_MAX; i++)
+		free(prop[i]);
+}
+
 /* put algorithm proposal into buffer */
 int
 kex_prop2buf(struct sshbuf *b, char *proposal[PROPOSAL_MAX])
diff --git a/usr.bin/ssh/kex.h b/usr.bin/ssh/kex.h
index 8363a6ea286..1a7584558ae 100644
--- a/usr.bin/ssh/kex.h
+++ b/usr.bin/ssh/kex.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: kex.h,v 1.117 2022/01/06 21:55:23 djm Exp $ */
+/* $OpenBSD: kex.h,v 1.118 2023/03/06 12:14:48 dtucker Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -175,6 +175,9 @@ int	 kex_names_valid(const char *);
 char	*kex_alg_list(char);
 char	*kex_names_cat(const char *, const char *);
 int	 kex_assemble_names(char **, const char *, const char *);
+void	 kex_proposal_populate_entries(struct ssh *, char *prop[PROPOSAL_MAX],
+    const char *, const char *, const char *, const char *, const char *);
+void	 kex_proposal_free_entries(char *prop[PROPOSAL_MAX]);
 
 int	 kex_exchange_identification(struct ssh *, int, const char *);
 
diff --git a/usr.bin/ssh/sshconnect2.c b/usr.bin/ssh/sshconnect2.c
index 1f93bb6fdad..10275515298 100644
--- a/usr.bin/ssh/sshconnect2.c
+++ b/usr.bin/ssh/sshconnect2.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect2.c,v 1.363 2023/03/03 02:34:29 dtucker Exp $ */
+/* $OpenBSD: sshconnect2.c,v 1.364 2023/03/06 12:14:48 dtucker Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  * Copyright (c) 2008 Damien Miller.  All rights reserved.
@@ -51,7 +51,6 @@
 #include "cipher.h"
 #include "sshkey.h"
 #include "kex.h"
-#include "myproposal.h"
 #include "sshconnect.h"
 #include "authfile.h"
 #include "dh.h"
@@ -216,24 +215,17 @@ void
 ssh_kex2(struct ssh *ssh, char *host, struct sockaddr *hostaddr, u_short port,
     const struct ssh_conn_info *cinfo)
 {
-	char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT };
-	char *s, *all_key;
-	char *prop_kex = NULL, *prop_enc = NULL, *prop_hostkey = NULL;
-	int r, use_known_hosts_order = 0;
+	char *myproposal[PROPOSAL_MAX];
+	char *s, *all_key, *hkalgs = NULL;
+	int r;
 
 	xxx_host = host;
 	xxx_hostaddr = hostaddr;
 	xxx_conn_info = cinfo;
 
-	/*
-	 * If the user has not specified HostkeyAlgorithms, or has only
-	 * appended or removed algorithms from that list then prefer algorithms
-	 * that are in the list that are supported by known_hosts keys.
-	 */
-	if (options.hostkeyalgorithms == NULL ||
-	    options.hostkeyalgorithms[0] == '-' ||
-	    options.hostkeyalgorithms[0] == '+')
-		use_known_hosts_order = 1;
+	if (options.rekey_limit || options.rekey_interval)
+		ssh_packet_set_rekey_limits(ssh, options.rekey_limit,
+		    options.rekey_interval);
 
 	/* Expand or fill in HostkeyAlgorithms */
 	all_key = sshkey_alg_list(0, 0, 1, ',');
@@ -244,29 +236,22 @@ ssh_kex2(struct ssh *ssh, char *host, struct sockaddr *hostaddr, u_short port,
 
 	if ((s = kex_names_cat(options.kex_algorithms, "ext-info-c")) == NULL)
 		fatal_f("kex_names_cat");
-	myproposal[PROPOSAL_KEX_ALGS] = prop_kex = compat_kex_proposal(ssh, s);
-	myproposal[PROPOSAL_ENC_ALGS_CTOS] =
-	    myproposal[PROPOSAL_ENC_ALGS_STOC] = prop_enc =
-	    compat_cipher_proposal(ssh, options.ciphers);
-	myproposal[PROPOSAL_COMP_ALGS_CTOS] =
-	    myproposal[PROPOSAL_COMP_ALGS_STOC] =
-	    (char *)compression_alg_list(options.compression);
-	myproposal[PROPOSAL_MAC_ALGS_CTOS] =
-	    myproposal[PROPOSAL_MAC_ALGS_STOC] = options.macs;
-	if (use_known_hosts_order) {
-		/* Query known_hosts and prefer algorithms that appear there */
-		myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = prop_hostkey =
-		    compat_pkalg_proposal(ssh,
-		    order_hostkeyalgs(host, hostaddr, port, cinfo));
-	} else {
-		/* Use specified HostkeyAlgorithms exactly */
-		myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = prop_hostkey =
-		    compat_pkalg_proposal(ssh, options.hostkeyalgorithms);
-	}
 
-	if (options.rekey_limit || options.rekey_interval)
-		ssh_packet_set_rekey_limits(ssh, options.rekey_limit,
-		    options.rekey_interval);
+	/*
+	 * If the user has not specified HostkeyAlgorithms, or has only
+	 * appended or removed algorithms from that list then prefer algorithms
+	 * that are in the list that are supported by known_hosts keys.
+	 */
+	if (options.hostkeyalgorithms == NULL ||
+	    options.hostkeyalgorithms[0] == '-' ||
+	    options.hostkeyalgorithms[0] == '+')
+		hkalgs = order_hostkeyalgs(host, hostaddr, port, cinfo);
+
+	kex_proposal_populate_entries(ssh, myproposal, s, options.ciphers,
+	    options.macs, compression_alg_list(options.compression),
+	    hkalgs ? hkalgs : options.hostkeyalgorithms);
+
+	free(hkalgs);
 
 	/* start key exchange */
 	if ((r = kex_setup(ssh, myproposal)) != 0)
@@ -288,6 +273,7 @@ ssh_kex2(struct ssh *ssh, char *host, struct sockaddr *hostaddr, u_short port,
 	ssh_dispatch_run_fatal(ssh, DISPATCH_BLOCK, &ssh->kex->done);
 
 	/* remove ext-info from the KEX proposals for rekeying */
+	free(myproposal[PROPOSAL_KEX_ALGS]);
 	myproposal[PROPOSAL_KEX_ALGS] =
 	    compat_kex_proposal(ssh, options.kex_algorithms);
 	if ((r = kex_prop2buf(ssh->kex->my, myproposal)) != 0)
@@ -301,10 +287,7 @@ ssh_kex2(struct ssh *ssh, char *host, struct sockaddr *hostaddr, u_short port,
 	    (r = ssh_packet_write_wait(ssh)) != 0)
 		fatal_fr(r, "send packet");
 #endif
-	/* Free only parts of proposal that were dynamically allocated here. */
-	free(prop_kex);
-	free(prop_enc);
-	free(prop_hostkey);
+	kex_proposal_free_entries(myproposal);
 }
 
 /*
diff --git a/usr.bin/ssh/sshd.c b/usr.bin/ssh/sshd.c
index 7ec2a4e34a9..e9219a3da14 100644
--- a/usr.bin/ssh/sshd.c
+++ b/usr.bin/ssh/sshd.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshd.c,v 1.598 2023/03/03 03:12:24 dtucker Exp $ */
+/* $OpenBSD: sshd.c,v 1.599 2023/03/06 12:14:48 dtucker Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -85,7 +85,6 @@
 #include "digest.h"
 #include "sshkey.h"
 #include "kex.h"
-#include "myproposal.h"
 #include "authfile.h"
 #include "pathnames.h"
 #include "atomicio.h"
@@ -2224,30 +2223,23 @@ sshd_hostkey_sign(struct ssh *ssh, struct sshkey *privkey,
 static void
 do_ssh2_kex(struct ssh *ssh)
 {
-	char *myproposal[PROPOSAL_MAX] = { KEX_SERVER };
+	char *hkalgs = NULL, *myproposal[PROPOSAL_MAX];
+	const char *compression = NULL;
 	struct kex *kex;
-	char *prop_kex = NULL, *prop_enc = NULL, *prop_hostkey = NULL;
 	int r;
 
-	myproposal[PROPOSAL_KEX_ALGS] = prop_kex = compat_kex_proposal(ssh,
-	    options.kex_algorithms);
-	myproposal[PROPOSAL_ENC_ALGS_CTOS] =
-	    myproposal[PROPOSAL_ENC_ALGS_STOC] = prop_enc =
-	    compat_cipher_proposal(ssh, options.ciphers);
-	myproposal[PROPOSAL_MAC_ALGS_CTOS] =
-	    myproposal[PROPOSAL_MAC_ALGS_STOC] = options.macs;
-
-	if (options.compression == COMP_NONE) {
-		myproposal[PROPOSAL_COMP_ALGS_CTOS] =
-		    myproposal[PROPOSAL_COMP_ALGS_STOC] = "none";
-	}
-
 	if (options.rekey_limit || options.rekey_interval)
 		ssh_packet_set_rekey_limits(ssh, options.rekey_limit,
 		    options.rekey_interval);
 
-	myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = prop_hostkey =
-	   compat_pkalg_proposal(ssh, list_hostkey_types());
+	if (options.compression == COMP_NONE)
+		compression = "none";
+	hkalgs = list_hostkey_types();
+
+	kex_proposal_populate_entries(ssh, myproposal, options.kex_algorithms,
+	    options.ciphers, options.macs, compression, hkalgs);
+
+	free(hkalgs);
 
 	/* start key exchange */
 	if ((r = kex_setup(ssh, myproposal)) != 0)
@@ -2280,9 +2272,7 @@ do_ssh2_kex(struct ssh *ssh)
 	    (r = ssh_packet_write_wait(ssh)) != 0)
 		fatal_fr(r, "send test");
 #endif
-	free(prop_kex);
-	free(prop_enc);
-	free(prop_hostkey);
+	kex_proposal_free_entries(myproposal);
 	debug("KEX done");
 }