[PATCH v5] http: add http.sslVerifyStatus to check stapled OCSP responses

[graysongordon-gl <graysongordon1@gmail.com>]

From: Grayson Gordon <graysongordon1@gmail.com>

git never sets CURLOPT_SSL_VERIFYSTATUS, so libcurl never requests the
OCSP "Certificate Status Request" extension and any stapled response a
server sends is ignored, including responses that explicitly state the
certificate has been revoked.

Add an http.sslVerifyStatus boolean that maps to
CURLOPT_SSL_VERIFYSTATUS.
http_options() is already the collect_fn for a urlmatch config, so the
per-URL form works with no changes:

    git config http.https://example.com/.sslVerifyStatus true

Defaults to false/"off". This is due to the nature of the OCSP protocol.
If enabled, git would expect to receive OCSP stapled responses. If the
stapled responses were not present, the connection would be blocked as
the status of the server's certificate could not be verified. This would
break connections to legitimate services that don't use OCSP as their
certificate revocation mechanism.

If the backend can't check the staple, curl_easy_setopt() returns
CURLE_NOT_BUILT_IN. Error message includes curl_easy_strerror() with
the option name to enable users to more easily identify a libcurl
built without status verification.

CURLOPT_SSL_VERIFYSTATUS has existed since libcurl 7.41.0, below our
7.61.0 floor, so no version guard is needed.

Tests are in t5551.

Signed-off-by: Grayson Gordon <graysongordon1@gmail.com>
---
 Documentation/config/http.adoc |  9 +++++++++
 http.c                         | 14 ++++++++++++++
 t/t5551-http-fetch-smart.sh    | 29 +++++++++++++++++++++++++++++
 3 files changed, 52 insertions(+)

diff --git a/Documentation/config/http.adoc b/Documentation/config/http.adoc
index 792a71b413..6bc2e3823d 100644
--- a/Documentation/config/http.adoc
+++ b/Documentation/config/http.adoc
@@ -196,6 +196,15 @@ http.sslVerify::
 	over HTTPS. Defaults to true. Can be overridden by the
 	`GIT_SSL_NO_VERIFY` environment variable.
 
+http.sslVerifyStatus::
+	Whether to check the revocation status of the server
+	certificate using the stapled OCSP response supplied during
+	the TLS handshake ("OCSP stapling"). Defaults to false.
++
+This is fail-closed: if the server staples no response, verification
+fails. Set it per remote, e.g.
+`http.https://example.com/.sslVerifyStatus`, rather than globally.
+
 http.sslCert::
 	File containing the SSL certificate when fetching or pushing
 	over HTTPS. Can be overridden by the `GIT_SSL_CERT` environment
diff --git a/http.c b/http.c
index caccf2108e..4a4dd40fe2 100644
--- a/http.c
+++ b/http.c
@@ -44,6 +44,7 @@ static CURL *curl_default;
 char curl_errorstr[CURL_ERROR_SIZE];
 
 static int curl_ssl_verify = -1;
+static int curl_ssl_verify_status;
 static int curl_ssl_try;
 static char *curl_http_version;
 static char *ssl_cert;
@@ -400,6 +401,10 @@ static int http_options(const char *var, const char *value,
 		curl_ssl_verify = git_config_bool(var, value);
 		return 0;
 	}
+	if (!strcmp("http.sslverifystatus", var)) {
+		curl_ssl_verify_status = git_config_bool(var, value);
+		return 0;
+	}
 	if (!strcmp("http.sslcipherlist", var))
 		return git_config_string(&ssl_cipherlist, var, value);
 	if (!strcmp("http.sslversion", var))
@@ -1133,6 +1138,15 @@ static CURL *get_curl_handle(void)
 		curl_easy_setopt(result, CURLOPT_SSL_VERIFYHOST, 2L);
 	}
 
+	if (curl_ssl_verify_status) {
+		CURLcode ret = curl_easy_setopt(result,
+						CURLOPT_SSL_VERIFYSTATUS, 1L);
+		if (ret != CURLE_OK)
+			die(_("http.sslVerifyStatus is set, but could not "
+			      "enable OCSP status verification: %s"),
+			    curl_easy_strerror(ret));
+	}
+
     if (curl_http_version) {
 		long opt;
 		if (!get_curl_http_version_opt(curl_http_version, &opt)) {
diff --git a/t/t5551-http-fetch-smart.sh b/t/t5551-http-fetch-smart.sh
index 805bec025c..75ab07f031 100755
--- a/t/t5551-http-fetch-smart.sh
+++ b/t/t5551-http-fetch-smart.sh
@@ -680,6 +680,35 @@ test_expect_success 'passing hostname resolution information works' '
 	git -c "http.curloptResolve=$BOGUS_HOST:$LIB_HTTPD_PORT:127.0.0.1" ls-remote "$BOGUS_HTTPD_URL/smart/repo.git" >/dev/null
 '
 
+test_lazy_prereq SSL_VERIFYSTATUS '
+	test "$HTTPD_PROTO" = "https" &&
+	test_might_fail git -c http.sslVerifyStatus=true \
+		ls-remote "$HTTPD_URL/smart/repo.git" 2>err &&
+	! grep "http.sslVerifyStatus is set" err
+'
+
+test_expect_success SSL_VERIFYSTATUS 'http.sslVerifyStatus=true fails without a staple' '
+	test_must_fail git -c http.sslVerifyStatus=true \
+		ls-remote "$HTTPD_URL/smart/repo.git"
+'
+
+test_expect_success SSL_VERIFYSTATUS 'http.sslVerifyStatus=false is a no-op' '
+	git -c http.sslVerifyStatus=false \
+		ls-remote "$HTTPD_URL/smart/repo.git" >actual &&
+	test_line_count -gt 0 actual
+'
+
+test_expect_success SSL_VERIFYSTATUS 'per-URL sslVerifyStatus applies to a matching URL' '
+	test_must_fail git -c "http.$HTTPD_URL/.sslVerifyStatus=true" \
+		ls-remote "$HTTPD_URL/smart/repo.git"
+'
+
+test_expect_success SSL_VERIFYSTATUS 'per-URL sslVerifyStatus is not applied to other URLs' '
+	git -c "http.https://example.com/.sslVerifyStatus=true" \
+		ls-remote "$HTTPD_URL/smart/repo.git" >actual &&
+	test_line_count -gt 0 actual
+'
+
 # here user%40host is the URL-encoded version of user@host,
 # which is our intentionally-odd username to catch parsing errors
 url_user=$HTTPD_URL_USER/auth/smart/repo.git
-- 
2.50.1 (Apple Git-155)