Re: bw/transport-protocol-policy

On 12/01, Jeff King wrote:

On Mon, Nov 28, 2016 at 04:15:08PM -0800, Junio C Hamano wrote:

quoted

* bw/transport-protocol-policy (2016-11-09) 2 commits
  (merged to 'next' on 2016-11-16 at 1391d3eeed)
 + transport: add protocol policy config option
 + lib-proto-disable: variable name fix

 Finer-grained control of what protocols are allowed for transports
 during clone/fetch/push have been enabled via a new configuration
 mechanism.

 Will cook in 'next'.

I was looking at the way the http code feeds protocol restrictions to
CURLOPT_REDIR_PROTOCOLS, and I think this topic is missing two elements:

  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.

  2. If your curl is too old to support CURLOPT_REDIR_PROTOCOLS, we will
     warn if there is a protocol whitelist in effect. But that check
     only covers the environment whitelist, and we do not warn if you
     restrict other protocols.

     I actually think this should probably just warn indiscriminately.
     Even without a Git protocol whitelist specified, the code serves to
     prevent curl from redirecting to bizarre protocols like smtp. The
     affected curl versions are from 2009 and prior, so I kind of doubt
     it matters much either way (I'm actually tempted to suggest we bump
     the minimum curl version there; there's a ton of #ifdef cruft going
     back to 2002-era versions of libcurl).

We should switch to warning all the time since this series adds in
default whitelisted/blacklisted protocols anyways.

-- 
Brandon Williams