upstream commit

Cap DH-GEX group size at 4kbits for Cisco implementations.
 Some of them will choke when asked for preferred sizes >4k instead of
 returning the 4k group that they do have.  bz#2209, ok djm@

Upstream-ID: 54b863a19713446b7431f9d06ad0532b4fcfef8d

compat.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: compat.c,v 1.93 2015/05/06 04:07:18 dtucker Exp $ */
+/* $OpenBSD: compat.c,v 1.94 2015/05/26 23:23:40 dtucker Exp $ */
 /*
  * Copyright (c) 1999, 2000, 2001, 2002 Markus Friedl.  All rights reserved.
  *
@@ -152,6 +152,7 @@ compat_datafellows(const char *version)
 		  "1.2.22*",		SSH_BUG_IGNOREMSG },
 		{ "1.3.2*",		/* F-Secure */
 					SSH_BUG_IGNOREMSG },
+		{ "Cisco-1.*",		SSH_BUG_DHGEX_LARGE },
 		{ "*SSH Compatible Server*",			/* Netscreen */
 					SSH_BUG_PASSWORDPAD },
 		{ "*OSU_0*,"

compat.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: compat.h,v 1.47 2015/04/10 05:16:50 dtucker Exp $ */
+/* $OpenBSD: compat.h,v 1.48 2015/05/26 23:23:40 dtucker Exp $ */
 
 /*
  * Copyright (c) 1999, 2000, 2001 Markus Friedl.  All rights reserved.
@@ -61,6 +61,7 @@
 #define SSH_BUG_DYNAMIC_RPORT	0x08000000
 #define SSH_BUG_CURVE25519PAD	0x10000000
 #define SSH_BUG_HOSTKEYS	0x20000000
+#define SSH_BUG_DHGEX_LARGE	0x40000000
 
 void     enable_compat13(void);
 void     enable_compat20(void);

kexgexc.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: kexgexc.c,v 1.21 2015/04/13 02:04:08 djm Exp $ */
+/* $OpenBSD: kexgexc.c,v 1.22 2015/05/26 23:23:40 dtucker Exp $ */
 /*
  * Copyright (c) 2000 Niels Provos.  All rights reserved.
  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
@@ -28,6 +28,7 @@
 
 #ifdef WITH_OPENSSL
 
+#include <sys/param.h>
 #include <sys/types.h>
 
 #include <openssl/dh.h>
@@ -65,6 +66,8 @@ kexgex_client(struct ssh *ssh)
 	kex->min = DH_GRP_MIN;
 	kex->max = DH_GRP_MAX;
 	kex->nbits = nbits;
+	if (datafellows & SSH_BUG_DHGEX_LARGE)
+		kex->nbits = MIN(kex->nbits, 4096);
 	/* New GEX request */
 	if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 ||
 	    (r = sshpkt_put_u32(ssh, kex->min)) != 0 ||