1 files changed, 86 insertions, 7 deletions

diff --git a/kex.c b/kex.c
index 4d8e6f536..39a6f98c4 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 1.109 2015/07/30 00:01:34 djm Exp $ */
 /*
  * Copyright (c) 2000, 2001 Markus Friedl.  All rights reserved.
  *
@@ -171,6 +171,68 @@ kex_names_valid(const char *names)
         return 1;
 }
 
+/*
+ * Concatenate algorithm names, avoiding duplicates in the process.
+ * Caller must free returned string.
+ */
+char *
+kex_names_cat(const char *a, const char *b)
+{
+        char *ret = NULL, *tmp = NULL, *cp, *p;
+        size_t len;
+
+        if (a == NULL || *a == '\0')
+                return NULL;
+        if (b == NULL || *b == '\0')
+                return strdup(a);
+        if (strlen(b) > 1024*1024)
+                return NULL;
+        len = strlen(a) + strlen(b) + 2;
+        if ((tmp = cp = strdup(b)) == NULL ||
+            (ret = calloc(1, len)) == NULL) {
+                free(tmp);
+                return NULL;
+        }
+        strlcpy(ret, a, len);
+        for ((p = strsep(&cp, ",")); p && *p != '\0'; (p = strsep(&cp, ","))) {
+                if (match_list(ret, p, NULL) != NULL)
+                        continue; /* Algorithm already present */
+                if (strlcat(ret, ",", len) >= len ||
+                    strlcat(ret, p, len) >= len) {
+                        free(tmp);
+                        free(ret);
+                        return NULL; /* Shouldn't happen */
+                }
+        }
+        free(tmp);
+        return ret;
+}
+
+/*
+ * Assemble a list of algorithms from a default list and a string from a
+ * configuration file. The user-provided string may begin with '+' to
+ * indicate that it should be appended to the default.
+ */
+int
+kex_assemble_names(const char *def, char **list)
+{
+        char *ret;
+
+        if (list == NULL || *list == NULL || **list == '\0') {
+                *list = strdup(def);
+                return 0;
+        }
+        if (**list != '+') {
+                return 0;
+        }
+
+        if ((ret = kex_names_cat(def, *list + 1)) == NULL)
+                return SSH_ERR_ALLOC_FAIL;
+        free(*list);
+        *list = ret;
+        return 0;
+}
+
 /* put algorithm proposal into buffer */
 int
 kex_prop2buf(struct sshbuf *b, char *proposal[PROPOSAL_MAX])
@@ -464,6 +526,7 @@ 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);
 }
 
@@ -642,17 +705,26 @@ 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,
@@ -660,10 +732,17 @@ 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 = peer[PROPOSAL_SERVER_HOST_KEY_ALGS];
+                peer[PROPOSAL_SERVER_HOST_KEY_ALGS] = NULL;
+                goto out;
+        }
         need = dh_need = 0;
         for (mode = 0; mode < MODE_MAX; mode++) {
                 newkeys = kex->newkeys[mode];