Re: [PATCH] transport: add core.allowProtocol config option

From

Jeff King <peff@peff.net>

Date

Nov 3, 2016, 18:24 UTC

Message-ID

<20161103182428.j3r574evsk7ypfie@sigill.intra.peff.net>

In-Reply-To

<20161103175327.nn2yasvlsxsy22be@sigill.intra.peff.net>

On Thu, Nov 03, 2016 at 01:53:27PM -0400, Jeff King wrote:

> I'd design the new system from scratch, and have it kick in _only_ when
> GIT_ALLOW_PROTOCOL is not set. That lets existing callers continue to
> have the safe behavior until they are ready to move to the new format.
> 
> Something like the patch below (which is just for illustration, and not
> tested beyond compilation).

Here's that same patch with a few tweaks:

  - it changes git-submodule to use the new, more flexible system (which
    also gets a it a lot more test coverage)

  - it tweaks two tests which use the "ext" helper to enable it (since
    it's blacklisted by default; I have mixed feelings on that, but I
    see why Blake wants it, as it would have protected things like "go
    get" out of the box).

  - it adds "file://" as a known-good protocol, even for submodules,
    which matches the current code.  I am not sure if this is reasonable
    or not. A malicious repository probably can't do much by pointing
    you to cloning your own repo as a submodule unless you then _also_
    run some arbitrary code to expose it, at which point it's generally
    game-over anyway.

    And I'd expect automated services (like GitHub Pages) to already
    have a cut-down whitelist via GIT_ALLOW_PROTOCOL (and I happen to
    know that it goes).

Do you have interest in picking this up and running with it?

-Peff

diff --git a/git-submodule.sh b/git-submodule.sh
index a024a135d..0a477b4c9 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -21,14 +21,10 @@ require_work_tree
 wt_prefix=$(git rev-parse --show-prefix)
 cd_to_toplevel
 
-# Restrict ourselves to a vanilla subset of protocols; the URLs
-# we get are under control of a remote repository, and we do not
-# want them kicking off arbitrary git-remote-* programs.
-#
-# If the user has already specified a set of allowed protocols,
-# we assume they know what they're doing and use that instead.
-: ${GIT_ALLOW_PROTOCOL=file:git:http:https:ssh}
-export GIT_ALLOW_PROTOCOL
+# Tell the rest of git that any URLs we get don't come
+# directly from the user, so it can apply policy as appropriate.
+GIT_PROTOCOL_FROM_USER=0
+export GIT_PROTOCOL_FROM_USER
 
 command=
 branch=
diff --git a/t/t5509-fetch-push-namespaces.sh b/t/t5509-fetch-push-namespaces.sh
index bc44ac36d..75c570adc 100755
--- a/t/t5509-fetch-push-namespaces.sh
+++ b/t/t5509-fetch-push-namespaces.sh
@@ -4,6 +4,7 @@ test_description='fetch/push involving ref namespaces'
 . ./test-lib.sh
 
 test_expect_success setup '
+	git config --global protocol.ext.allow user &&
 	test_tick &&
 	git init original &&
 	(
diff --git a/t/t5802-connect-helper.sh b/t/t5802-connect-helper.sh
index b7a7f9d58..c6c266187 100755
--- a/t/t5802-connect-helper.sh
+++ b/t/t5802-connect-helper.sh
@@ -4,6 +4,7 @@ test_description='ext::cmd remote "connect" helper'
 . ./test-lib.sh
 
 test_expect_success setup '
+	git config --global protocol.ext.allow user &&
 	test_tick &&
 	git commit --allow-empty -m initial &&
 	test_tick &&
diff --git a/transport.c b/transport.c
index d57e8dec2..cd603fbf5 100644
--- a/transport.c
+++ b/transport.c
@@ -664,10 +664,70 @@ static const struct string_list *protocol_whitelist(void)
 	return enabled ? &allowed : NULL;
 }
 
+enum protocol_allow_config {
+	PROTOCOL_ALLOW_NEVER = 0,
+	PROTOCOL_ALLOW_USER_ONLY,
+	PROTOCOL_ALLOW_ALWAYS
+};
+
+static enum protocol_allow_config parse_protocol_config(const char *key,
+							const char *value)
+{
+	if (!strcasecmp(value, "always"))
+		return PROTOCOL_ALLOW_ALWAYS;
+	else if (!strcasecmp(value, "never"))
+		return PROTOCOL_ALLOW_NEVER;
+	else if (!strcasecmp(value, "user"))
+		return PROTOCOL_ALLOW_USER_ONLY;
+
+	/* XXX maybe also interpret git_config_bool() here? */
+	die("unknown value for config '%s': %s", key, value);
+}
+
+static enum protocol_allow_config get_protocol_config(const char *type)
+{
+	char *key = xstrfmt("protocol.%s.allow", type);
+	char *value;
+
+	if (!git_config_get_string(key, &value)) {
+		enum protocol_allow_config ret =
+			parse_protocol_config(key, value);
+		free(key);
+		free(value);
+		return ret;
+	}
+	free(key);
+
+	/* known safe */
+	if (!strcmp(type, "http") ||
+	    !strcmp(type, "https") ||
+	    !strcmp(type, "git") ||
+	    !strcmp(type, "ssh") ||
+	    !strcmp(type, "file"))
+		return PROTOCOL_ALLOW_ALWAYS;
+
+	/* known scary; err on the side of caution */
+	if (!strcmp(type, "ext"))
+		return PROTOCOL_ALLOW_NEVER;
+
+	/* unknown; let them be used only directly by the user */
+	return PROTOCOL_ALLOW_USER_ONLY;
+}
+
 int is_transport_allowed(const char *type)
 {
-	const struct string_list *allowed = protocol_whitelist();
-	return !allowed || string_list_has_string(allowed, type);
+	const struct string_list *whitelist = protocol_whitelist();
+	if (whitelist)
+		return string_list_has_string(whitelist, type);
+
+	switch (get_protocol_config(type)) {
+	case PROTOCOL_ALLOW_ALWAYS:
+		return 1;
+	case PROTOCOL_ALLOW_NEVER:
+		return 0;
+	case PROTOCOL_ALLOW_USER_ONLY:
+		return git_env_bool("GIT_PROTOCOL_FROM_USER", 1);
+	}
 }
 
 void transport_check_allowed(const char *type)