From ecf301d7dbd173cc18f86026ecf88597b15a7c69 Mon Sep 17 00:00:00 2001
From: Hans Nilsson <hans@erlang.org>
Date: Thu, 26 Nov 2015 10:45:13 +0100
Subject: ssh: Improve group selection

Now it chooses the first found if no exact match.
---
 lib/ssh/src/ssh_transport.erl | 42 +++++++++++++++---------------------------
 1 file changed, 15 insertions(+), 27 deletions(-)

(limited to 'lib/ssh')

diff --git a/lib/ssh/src/ssh_transport.erl b/lib/ssh/src/ssh_transport.erl
index 1fbe50e758..e3ee399b8e 100644
--- a/lib/ssh/src/ssh_transport.erl
+++ b/lib/ssh/src/ssh_transport.erl
@@ -1378,35 +1378,23 @@ dh_gex_default_groups() -> ?dh_default_groups.
 dh_gex_group(Min, N, Max, undefined) ->
     dh_gex_group(Min, N, Max, dh_gex_default_groups());
 dh_gex_group(Min, N, Max, Groups) ->
-    %% First try to find an exact match. If not an exact match, select the largest possible.
-    {_,Group} =
-	lists:foldl(
-	  fun(_, {I,G}) when I==N ->
-		  %% If we have an exact match already: use that one
-		  {I,G};
-	     ({I,G}, _) when I==N ->
-		  %% If we now found an exact match: use that very one
-		  {I,G};
-	     ({I,G}, {Imax,_Gmax}) when Min=<I,I=<Max, % a) {I,G} fullfills the requirements
-				        I>Imax ->      % b) {I,G} is larger than current max
-		  %% A group within the limits and better than the one we have
-		  {I,G};
-	     (_, IGmax) ->
-		  %% Keep the one we have
-		  IGmax
-	  end, {-1,undefined}, Groups),
-
-    case Group of
-	undefined ->
-	    throw(#ssh_msg_disconnect{
-		     code = ?SSH_DISCONNECT_PROTOCOL_ERROR,
-		     description = "No possible diffie-hellman-group-exchange group found", 
-		     language = ""});
-	_ ->
-	    Group
+    %% Try to find an exact match. If not an exact match, select the first found.
+    case lists:keyfind(N, 1, Groups) of
+	{N,Grp} -> 
+	    Grp;
+	false -> 
+	    case lists:dropwhile(fun({I,_}) -> I < Min-1 orelse I > Max+1 end,
+				 Groups) of
+		[{_,Grp}|_] ->
+		    Grp;
+		[] ->
+		    throw(#ssh_msg_disconnect{
+			     code = ?SSH_DISCONNECT_PROTOCOL_ERROR,
+			     description = "No possible diffie-hellman-group-exchange group found", 
+			     language = ""})
+	    end
     end.
 
-
 generate_key(Algorithm, Args) ->
     {Public,Private} = crypto:generate_key(Algorithm, Args),
     {crypto:bytes_to_integer(Public), crypto:bytes_to_integer(Private)}.
-- 
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