From 2d22150270739cd29d0ac6bc329e0a2e2910d7d9 Mon Sep 17 00:00:00 2001
From: Petr Stodulka <pstodulk@redhat.com>
Date: Fri, 23 Oct 2015 17:36:57 +0200
Subject: [PATCH 4/5] http-limit-redirection-to-protocol-whitelist

Previously, libcurl would follow redirection to any protocol
it was compiled for support with. This is desirable to allow
redirection from HTTP to HTTPS. However, it would even
successfully allow redirection from HTTP to SFTP, a protocol
that git does not otherwise support at all. Furthermore
git's new protocol-whitelisting could be bypassed by
following a redirect within the remote helper, as it was
only enforced at transport selection time.

This patch limits redirects within libcurl to HTTP, HTTPS,
FTP and FTPS. If there is a protocol-whitelist present, this
list is limited to those also allowed by the whitelist. As
redirection happens from within libcurl, it is impossible
for an HTTP redirect to a protocol implemented within
another remote helper.

When the curl version git was compiled with is too old to
support restrictions on protocol redirection, we warn the
user if GIT_ALLOW_PROTOCOL restrictions were requested. This
is a little inaccurate, as even without that variable in the
environment, we would still restrict SFTP, etc, and we do
not warn in that case. But anything else means we would
literally warn every time git accesses an http remote.
---
 http.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/http.c b/http.c
index 92aba59..235c2d5 100644
--- a/http.c
+++ b/http.c
@@ -6,6 +6,7 @@
 #include "credential.h"
 #include "version.h"
 #include "pkt-line.h"
+#include "transport.h"
 
 int active_requests;
 int http_is_verbose;
@@ -252,6 +253,7 @@ static int has_cert_password(void)
 static CURL *get_curl_handle(void)
 {
 	CURL *result = curl_easy_init();
+	long allowed_protocols = 0;
 
 	if (!curl_ssl_verify) {
 		curl_easy_setopt(result, CURLOPT_SSL_VERIFYPEER, 0);
@@ -301,6 +303,21 @@ static CURL *get_curl_handle(void)
 #elif LIBCURL_VERSION_NUM >= 0x071101
 	curl_easy_setopt(result, CURLOPT_POST301, 1);
 #endif
+#if LIBCURL_VERSION_NUM >= 0x071304
+	if (is_transport_allowed("http"))
+		allowed_protocols |= CURLPROTO_HTTP;
+	if (is_transport_allowed("https"))
+		allowed_protocols |= CURLPROTO_HTTPS;
+	if (is_transport_allowed("ftp"))
+		allowed_protocols |= CURLPROTO_FTP;
+	if (is_transport_allowed("ftps"))
+		allowed_protocols |= CURLPROTO_FTPS;
+	curl_easy_setopt(result, CURLOPT_REDIR_PROTOCOLS, allowed_protocols);
+#else
+	if (transport_restrict_protocols())
+		warning("protocol restrictions not applied to curl redirects because\n"
+			"your curl version is too old (>= 7.19.4)");
+#endif
 
 	if (getenv("GIT_CURL_VERBOSE"))
 		curl_easy_setopt(result, CURLOPT_VERBOSE, 1);
-- 
2.1.0