3 files changed, 38 insertions, 9 deletions

diff --git a/kex.c b/kex.c
index dbc55ef7e..5e8b51394 100644
--- a/kex.c
+++ b/kex.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kex.c,v 1.106 2015/04/17 13:25:52 djm Exp $ */
+/* $OpenBSD: kex.c,v 1.107 2015/07/29 04:43:06 djm Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  *
@@ -448,6 +448,7 @@ kex_free(struct kex *kex)
         free(kex->session_id);
         free(kex->client_version_string);
         free(kex->server_version_string);
+        free(kex->failed_choice);
         free(kex);
 }
 
@@ -626,17 +627,26 @@ kex_choose_conf(struct ssh *ssh)
                 nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
                 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
                 if ((r = choose_enc(&newkeys->enc, cprop[nenc],
-                    sprop[nenc])) != 0)
+                    sprop[nenc])) != 0) {
+                        kex->failed_choice = peer[nenc];
+                        peer[nenc] = NULL;
                         goto out;
+                }
                 authlen = cipher_authlen(newkeys->enc.cipher);
                 /* ignore mac for authenticated encryption */
                 if (authlen == 0 &&
                     (r = choose_mac(ssh, &newkeys->mac, cprop[nmac],
-                    sprop[nmac])) != 0)
+                    sprop[nmac])) != 0) {
+                        kex->failed_choice = peer[nmac];
+                        peer[nmac] = NULL;
                         goto out;
+                }
                 if ((r = choose_comp(&newkeys->comp, cprop[ncomp],
-                    sprop[ncomp])) != 0)
+                    sprop[ncomp])) != 0) {
+                        kex->failed_choice = peer[ncomp];
+                        peer[ncomp] = NULL;
                         goto out;
+                }
                 debug("kex: %s %s %s %s",
                     ctos ? "client->server" : "server->client",
                     newkeys->enc.name,
@@ -644,10 +654,17 @@ kex_choose_conf(struct ssh *ssh)
                     newkeys->comp.name);
         }
         if ((r = choose_kex(kex, cprop[PROPOSAL_KEX_ALGS],
-            sprop[PROPOSAL_KEX_ALGS])) != 0 ||
-            (r = choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
-            sprop[PROPOSAL_SERVER_HOST_KEY_ALGS])) != 0)
+            sprop[PROPOSAL_KEX_ALGS])) != 0) {
+                kex->failed_choice = peer[PROPOSAL_KEX_ALGS];
+                peer[PROPOSAL_KEX_ALGS] = NULL;
                 goto out;
+        }
+        if ((r = choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
+            sprop[PROPOSAL_SERVER_HOST_KEY_ALGS])) != 0) {
+                kex->failed_choice = cprop[PROPOSAL_SERVER_HOST_KEY_ALGS];
+                cprop[PROPOSAL_SERVER_HOST_KEY_ALGS] = NULL;
+                goto out;
+        }
         need = dh_need = 0;
         for (mode = 0; mode < MODE_MAX; mode++) {
                 newkeys = kex->newkeys[mode];
diff --git a/kex.h b/kex.h
index f70b81fc1..fea5a75dd 100644
--- a/kex.h
+++ b/kex.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: kex.h,v 1.71 2015/02/16 22:13:32 djm Exp $ */
+/* $OpenBSD: kex.h,v 1.72 2015/07/29 04:43:06 djm Exp $ */
 
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
@@ -141,6 +141,7 @@ struct kex {
         int     ec_nid;
         char    *client_version_string;
         char    *server_version_string;
+        char    *failed_choice;
         int     (*verify_host_key)(struct sshkey *, struct ssh *);
         struct sshkey *(*load_host_public_key)(int, int, struct ssh *);
         struct sshkey *(*load_host_private_key)(int, int, struct ssh *);
diff --git a/packet.c b/packet.c
index a7727ef65..6008c2d94 100644
--- a/packet.c
+++ b/packet.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: packet.c,v 1.212 2015/05/01 07:10:01 djm Exp $ */
+/* $OpenBSD: packet.c,v 1.213 2015/07/29 04:43:06 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1933,6 +1933,17 @@ sshpkt_fatal(struct ssh *ssh, const char *tag, int r)
                         cleanup_exit(255);
                 }
                 /* FALLTHROUGH */
+        case SSH_ERR_NO_CIPHER_ALG_MATCH:
+        case SSH_ERR_NO_MAC_ALG_MATCH:
+        case SSH_ERR_NO_COMPRESS_ALG_MATCH:
+        case SSH_ERR_NO_KEX_ALG_MATCH:
+        case SSH_ERR_NO_HOSTKEY_ALG_MATCH:
+                if (ssh && ssh->kex && ssh->kex->failed_choice) {
+                        fatal("Unable to negotiate with %.200s: %s. "
+                            "Their offer: %s", ssh_remote_ipaddr(ssh),
+                            ssh_err(r), ssh->kex->failed_choice);
+                }
+                /* FALLTHROUGH */
         default:
                 fatal("%s%sConnection to %.200s: %s",
                     tag != NULL ? tag : "", tag != NULL ? ": " : "",