From df7bb23744d35804e144f4257c812994afcb22e8 Mon Sep 17 00:00:00 2001
From: Damien Miller <djm@mindrot.org>
Date: Tue, 17 Jan 2012 20:57:35 +1100
Subject: [PATCH] defatal kex_send_kexinit

---
 ssh/clientloop.c |  8 ++++++--
 ssh/kex.c        | 50 ++++++++++++++++++++++++------------------------
 ssh/kex.h        |  2 +-
 ssh/serverloop.c |  8 ++++++--
 4 files changed, 38 insertions(+), 30 deletions(-)

diff --git a/ssh/clientloop.c b/ssh/clientloop.c
index 406660c..3db8f0a 100644
--- a/ssh/clientloop.c
+++ b/ssh/clientloop.c
@@ -104,6 +104,7 @@
 #include "match.h"
 #include "msg.h"
 #include "roaming.h"
+#include "err.h"
 
 /* import options */
 extern Options options;
@@ -1380,7 +1381,7 @@ client_loop(int have_pty, int escape_char_arg, int ssh2_chan_id)
 {
 	fd_set *readset = NULL, *writeset = NULL;
 	double start_time, total_time;
-	int max_fd = 0, max_fd2 = 0, len, rekeying = 0;
+	int r, max_fd = 0, max_fd2 = 0, len, rekeying = 0;
 	u_int64_t ibytes, obytes;
 	u_int nalloc = 0;
 	char buf[100];
@@ -1511,7 +1512,10 @@ client_loop(int have_pty, int escape_char_arg, int ssh2_chan_id)
 			if (need_rekeying || packet_need_rekeying()) {
 				debug("need rekeying");
 				active_state->kex->done = 0;
-				kex_send_kexinit(active_state);
+				if ((r = kex_send_kexinit(active_state)) != 0) {
+					fatal("%s: kex_send_kexinit: %s",
+					    __func__, ssh_err(r));
+				}
 				need_rekeying = 0;
 			}
 		}
diff --git a/ssh/kex.c b/ssh/kex.c
index 26a7d26..7466ee0 100644
--- a/ssh/kex.c
+++ b/ssh/kex.c
@@ -189,39 +189,36 @@ kex_input_newkeys(int type, u_int32_t seq, struct ssh *ssh)
 	return 0;
 }
 
-void
+int
 kex_send_kexinit(struct ssh *ssh)
 {
-	u_int32_t rnd = 0;
 	u_char *cookie;
-	u_int i;
 	Kex *kex = ssh->kex;
+	int r;
 
-	if (kex == NULL) {
-		error("kex_send_kexinit: no kex, cannot rekey");
-		return;
-	}
-	if (kex->flags & KEX_INIT_SENT) {
-		debug("KEX_INIT_SENT");
-		return;
-	}
+	if (kex == NULL)
+		return SSH_ERR_INTERNAL_ERROR;
+	if (kex->flags & KEX_INIT_SENT)
+		return 0;
 	kex->done = 0;
 
 	/* generate a random cookie */
 	if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
-		fatal("kex_send_kexinit: kex proposal too short");
-	cookie = buffer_ptr(&kex->my);
-	for (i = 0; i < KEX_COOKIE_LEN; i++) {
-		if (i % 4 == 0)
-			rnd = arc4random();
-		cookie[i] = rnd;
-		rnd >>= 8;
-	}
-	ssh_packet_start(ssh, SSH2_MSG_KEXINIT);
-	ssh_packet_put_raw(ssh, buffer_ptr(&kex->my), buffer_len(&kex->my));
-	ssh_packet_send(ssh);
+		return SSH_ERR_INVALID_FORMAT;
+	if ((cookie = sshbuf_ptr(&kex->my)) == NULL)
+		return SSH_ERR_INTERNAL_ERROR;
+	arc4random_buf(cookie, KEX_COOKIE_LEN);
+
+	if ((r = sshpkt_start(ssh, SSH2_MSG_KEXINIT)) != 0)
+		return r;
+	if ((r = sshpkt_put(ssh, buffer_ptr(&kex->my),
+	    buffer_len(&kex->my))) != 0)
+		return r;
+	if ((r = sshpkt_send(ssh)) != 0)
+		return r;
 	debug("SSH2_MSG_KEXINIT sent");
 	kex->flags |= KEX_INIT_SENT;
+	return 0;
 }
 
 /* ARGSUSED */
@@ -254,8 +251,10 @@ kex_input_kexinit(int type, u_int32_t seq, struct ssh *ssh)
 			return r;
 
 	/* XXX check error */
-	if (!(kex->flags & KEX_INIT_SENT))
-		kex_send_kexinit(ssh);
+	if (!(kex->flags & KEX_INIT_SENT)) {
+		if ((r = kex_send_kexinit(ssh)) != 0)
+			return r;
+	}
 	kex_choose_conf(ssh);
 
 	if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
@@ -296,7 +295,8 @@ Kex *
 kex_setup(struct ssh *ssh, char *proposal[PROPOSAL_MAX])
 {
 	ssh->kex = kex_new(ssh, proposal);
-	kex_send_kexinit(ssh);				/* we start */
+	if (kex_send_kexinit(ssh) != 0)		/* we start */
+		return NULL;	/* XXX */
 	return ssh->kex;
 }
 
diff --git a/ssh/kex.h b/ssh/kex.h
index caac4de..e1b5e87 100644
--- a/ssh/kex.h
+++ b/ssh/kex.h
@@ -144,7 +144,7 @@ char   **kex_buf2prop(Buffer *, int *);
 void	 kex_prop2buf(Buffer *, char *proposal[PROPOSAL_MAX]);
 void	 kex_prop_free(char **);
 
-void	 kex_send_kexinit(struct ssh *);
+int	 kex_send_kexinit(struct ssh *);
 int	 kex_input_kexinit(int, u_int32_t, struct ssh *);
 int	 kex_derive_keys(struct ssh *, u_char *, u_int, BIGNUM *);
 
diff --git a/ssh/serverloop.c b/ssh/serverloop.c
index 9730077..cf156b1 100644
--- a/ssh/serverloop.c
+++ b/ssh/serverloop.c
@@ -77,6 +77,7 @@
 #include "serverloop.h"
 #include "misc.h"
 #include "roaming.h"
+#include "err.h"
 
 extern ServerOptions options;
 
@@ -787,7 +788,7 @@ void
 server_loop2(Authctxt *authctxt)
 {
 	fd_set *readset = NULL, *writeset = NULL;
-	int rekeying = 0, max_fd, nalloc = 0;
+	int r, rekeying = 0, max_fd, nalloc = 0;
 
 	debug("Entering interactive session for SSH2.");
 
@@ -832,7 +833,10 @@ server_loop2(Authctxt *authctxt)
 			if (packet_need_rekeying()) {
 				debug("need rekeying");
 				active_state->kex->done = 0;
-				kex_send_kexinit(active_state);
+				if ((r = kex_send_kexinit(active_state)) != 0) {
+					fatal("%s: kex_send_kexinit: %s",
+					    __func__, ssh_err(r));
+				}
 			}
 		}
 		process_input(readset);