- provos@cvs.openbsd.org 2001/03/27 17:46:50

     [compat.c compat.h dh.c dh.h ssh2.h sshconnect2.c sshd.c version.h]
     make dh group exchange more flexible, allow min and max group size,
     okay markus@, deraadt@

1 files changed, 29 insertions, 5 deletions

diff --git a/sshd.c b/sshd.c
index 961aeeaa0..65cb832d4 100644
--- a/sshd.c
+++ b/sshd.c
@@ -40,7 +40,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: sshd.c,v 1.180 2001/03/27 10:34:08 markus Exp $");
+RCSID("$OpenBSD: sshd.c,v 1.181 2001/03/27 17:46:49 provos Exp $");
 
 #include <openssl/dh.h>
 #include <openssl/bn.h>
@@ -1614,7 +1614,7 @@ ssh_dhgex_server(Kex *kex, Buffer *client_kexinit, Buffer *server_kexinit)
         int i;
 #endif
         int payload_len, dlen;
-        int slen, nbits;
+        int slen, nbits, type, min, max;
         u_char *signature = NULL;
         u_char *server_host_key_blob = NULL;
         u_int sbloblen;
@@ -1632,9 +1632,33 @@ ssh_dhgex_server(Kex *kex, Buffer *client_kexinit, Buffer *server_kexinit)
 
 /* KEXDHGEX */
         debug("Wait SSH2_MSG_KEX_DH_GEX_REQUEST.");
-        packet_read_expect(&payload_len, SSH2_MSG_KEX_DH_GEX_REQUEST);
-        nbits = packet_get_int();
-        dh = choose_dh(nbits);
+        type = packet_read(&payload_len);
+        if (type != SSH2_MSG_KEX_DH_GEX_REQUEST_OLD &&
+            type != SSH2_MSG_KEX_DH_GEX_REQUEST)
+                packet_disconnect("Protocol error: expected type %d or %d, got %d",
+                    SSH2_MSG_KEX_DH_GEX_REQUEST_OLD,
+                    SSH2_MSG_KEX_DH_GEX_REQUEST,
+                    type);
+        if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) {
+                nbits = packet_get_int();
+                min = DH_GRP_MIN;
+                max = DH_GRP_MAX;
+        } else {
+                min = packet_get_int();
+                nbits = packet_get_int();
+                max = packet_get_int();
+
+                min = MAX(DH_GRP_MIN, min);
+                max = MIN(DH_GRP_MAX, max);
+        }
+
+        if (max < min || nbits < min || max < nbits)
+                fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
+                    min, nbits, max);
+
+        dh = choose_dh(min, nbits, max);
+        if (dh == NULL)
+                packet_disconnect("Protocol error: no matching DH grp found");
 
         debug("Sending SSH2_MSG_KEX_DH_GEX_GROUP.");
         packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);