[PATCH v2] http: Control GSSAPI credential delegation.

[Petr Stodulka <pstodulk@redhat.com>]

Delegation of credentials is disabled by default in libcurl since
version 7.21.7 due to security vulnerability CVE-2011-2192. Which
makes troubles with GSS/kerberos authentication when delegation
of credentials is required. This can be changed with option
CURLOPT_GSSAPI_DELEGATION in libcurl with set expected parameter
since libcurl version 7.22.0.

This patch provides new configuration variable http.delegation
which corresponds to curl parameter "--delegation" (see man 1 curl).

The following values are supported:

* none (default).
* policy
* always

Signed-off-by: Petr Stodulka <pstodulk@redhat.com>
---
 Documentation/config.txt | 14 ++++++++++++++
 http.c                   | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index e78293b..a179474 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1736,6 +1736,20 @@ http.emptyAuth::
 	a username in the URL, as libcurl normally requires a username for
 	authentication.
 
+http.delegation::
+	Control GSSAPI credential delegation. The delegation is disabled
+	by default in libcurl since version 7.21.7. Set parameter to tell
+	the server what it is allowed to delegate when it comes to user
+	credentials. Used with GSS/kerberos. Possible values are:
++
+--
+* `none` - Don't allow any delegation.
+* `policy` - Delegates if and only if the OK-AS-DELEGATE flag is set in the
+  Kerberos service ticket, which is a matter of realm policy.
+* `always` - Unconditionally allow the server to delegate.
+--
+
+
 http.extraHeader::
 	Pass an additional HTTP header when communicating with a server.  If
 	more than one such entry exists, all of them are added as extra
diff --git a/http.c b/http.c
index 82ed542..0c65639 100644
--- a/http.c
+++ b/http.c
@@ -90,6 +90,18 @@ static struct {
 	 * here, too
 	 */
 };
+#if LIBCURL_VERSION_NUM >= 0x071600
+static const char *curl_deleg;
+static struct {
+	const char *name;
+	long curl_deleg_param;
+} curl_deleg_levels[] = {
+	{ "none", CURLGSSAPI_DELEGATION_NONE },
+	{ "policy", CURLGSSAPI_DELEGATION_POLICY_FLAG },
+	{ "always", CURLGSSAPI_DELEGATION_FLAG },
+};
+#endif
+
 static struct credential proxy_auth = CREDENTIAL_INIT;
 static const char *curl_proxyuserpwd;
 static const char *curl_cookie_file;
@@ -323,6 +335,15 @@ static int http_options(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (!strcmp("http.delegation", var)) {
+#if LIBCURL_VERSION_NUM >= 0x071600
+		return git_config_string(&curl_deleg, var, value);
+#else
+		warning(_("Delegation control is not supported with cURL < 7.22.0"));
+		return 0;
+#endif
+	}
+
 	if (!strcmp("http.pinnedpubkey", var)) {
 #if LIBCURL_VERSION_NUM >= 0x072c00
 		return git_config_pathname(&ssl_pinnedkey, var, value);
@@ -629,6 +650,22 @@ static CURL *get_curl_handle(void)
 	curl_easy_setopt(result, CURLOPT_HTTPAUTH, CURLAUTH_ANY);
 #endif
 
+#if LIBCURL_VERSION_NUM >= 0x071600
+	if (curl_deleg) {
+		int i;
+		for (i = 0; i < ARRAY_SIZE(curl_deleg_levels); i++) {
+			if (!strcmp(curl_deleg, curl_deleg_levels[i].name)) {
+				curl_easy_setopt(result, CURLOPT_GSSAPI_DELEGATION,
+						curl_deleg_levels[i].curl_deleg_param);
+				break;
+			}
+		}
+		if (i == ARRAY_SIZE(curl_deleg_levels))
+			warning("Unknown delegation method '%s': using default",
+				curl_deleg);
+	}
+#endif
+
 	if (http_proactive_auth)
 		init_curl_http_auth(result);
 
-- 
2.5.5