Re: bw/transport-protocol-policy

On 12/01, Jeff King wrote:

On Thu, Dec 01, 2016 at 10:14:15AM -0800, Brandon Williams wrote:

quoted

quoted

  1. The new policy config lets you say "only allow this protocol when
     the user specifies it". But when http.c calls is_transport_allowed(),
     the latter has no idea that we are asking it about potential
     redirects (which obviously do _not_ come from the user), and would
     erroneously allow them.

     I think this needs fixed before the topic is merged. It's not a
     regression, as it only comes into play if you use the new policy
     config. But it is a minor security hole in the new feature.

I agree and it should be an easy fix.  We can just add a parameter like
so:

diff --git a/transport.c b/transport.c
index 2c0ec76..d38d50f 100644
--- a/transport.c
+++ b/transport.c

@@ -723,7 +723,7 @@ static enum protocol_allow_config get_protocol_config(const char *type)
 	return PROTOCOL_ALLOW_USER_ONLY;
 }
 
-int is_transport_allowed(const char *type)
+int is_transport_allowed(const char *type, int redirect)
 {
 	const struct string_list *whitelist = protocol_whitelist();
 	if (whitelist)

@@ -735,7 +735,7 @@ int is_transport_allowed(const char *type)
 	case PROTOCOL_ALLOW_NEVER:
 		return 0;
 	case PROTOCOL_ALLOW_USER_ONLY:
-		return git_env_bool("GIT_PROTOCOL_FROM_USER", 1);
+		return git_env_bool("GIT_PROTOCOL_FROM_USER", !redirect);
 	}
 
 	die("BUG: invalid protocol_allow_config type");

That way the libcurl code can say it is asking if it is ok to redirect
to that protocol.

I wouldn't expect anyone to ever set GIT_PROTOCOL_FROM_USER=1, but it
does behave in a funny way here, overriding the "redirect" flag. I think
we'd want something more like:

  if (redirect < 0)
	redirect = git_env_bool("GIT_PROTOCOL_FROM_USER", 1);

and then pass in "-1" from transport_check_allowed().

I don't think I quite follow your solution but I came up with this:

  case PROTOCOL_ALLOW_USER_ONLY:
    return redirect ? 0 : git_env_bool("GIT_PROTOCOL_FROM_USER", 1);

Which should address the same issue.

-- 
Brandon Williams