Merge branch 'jk/http-walker-limit-redirect-2.9'

Transport with dumb http can be fooled into following foreign URLs
that the end user does not intend to, especially with the server
side redirects and http-alternates mechanism, which can lead to
security issues.  Tighten the redirection and make it more obvious
to the end user when it happens.

* jk/http-walker-limit-redirect-2.9:
  http: treat http-alternates like redirects
  http: make redirects more obvious
  remote-curl: rename shadowed options variable
  http: always update the base URL for redirects
  http: simplify update_url_from_redirect

Documentation/config.txt

@@ -1891,6 +1891,16 @@ http.userAgent::
 	of common USER_AGENT strings (but not including those like git/1.7.1).
 	Can be overridden by the `GIT_HTTP_USER_AGENT` environment variable.
 
+http.followRedirects::
+	Whether git should follow HTTP redirects. If set to `true`, git
+	will transparently follow any redirect issued by a server it
+	encounters. If set to `false`, git will treat all redirects as
+	errors. If set to `initial`, git will follow redirects only for
+	the initial request to a remote, but not for subsequent
+	follow-up HTTP requests. Since git uses the redirected URL as
+	the base for the follow-up requests, this is generally
+	sufficient. The default is `initial`.
+
 http.<url>.*::
 	Any of the http.* options above can be applied selectively to some URLs.
 	For a config key to match a URL, each element of the config key is

http-walker.c

@@ -274,9 +274,8 @@ static void process_alternates_response(void *callback_data)
 				struct strbuf target = STRBUF_INIT;
 				strbuf_add(&target, base, serverlen);
 				strbuf_add(&target, data + i, posn - i - 7);
-				if (walker->get_verbosely)
-					fprintf(stderr, "Also look at %s\n",
-						target.buf);
+				warning("adding alternate object store: %s",
+					target.buf);
 				newalt = xmalloc(sizeof(*newalt));
 				newalt->next = NULL;
 				newalt->base = strbuf_detach(&target, NULL);
@@ -302,6 +301,9 @@ static void fetch_alternates(struct walker *walker, const char *base)
 	struct alternates_request alt_req;
 	struct walker_data *cdata = walker->data;
 
+	if (http_follow_config != HTTP_FOLLOW_ALWAYS)
+		return;
+
 	/*
 	 * If another request has already started fetching alternates,
 	 * wait for them to arrive and return to processing this request's

http.c

@@ -111,6 +111,8 @@ static int http_proactive_auth;
 static const char *user_agent;
 static int curl_empty_auth;
 
+enum http_follow_config http_follow_config = HTTP_FOLLOW_INITIAL;
+
 #if LIBCURL_VERSION_NUM >= 0x071700
 /* Use CURLOPT_KEYPASSWD as is */
 #elif LIBCURL_VERSION_NUM >= 0x070903
@@ -366,6 +368,16 @@ static int http_options(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (!strcmp("http.followredirects", var)) {
+		if (value && !strcmp(value, "initial"))
+			http_follow_config = HTTP_FOLLOW_INITIAL;
+		else if (git_config_bool(var, value))
+			http_follow_config = HTTP_FOLLOW_ALWAYS;
+		else
+			http_follow_config = HTTP_FOLLOW_NONE;
+		return 0;
+	}
+
 	/* Fall back on the default ones */
 	return git_default_config(var, value, cb);
 }
@@ -717,7 +729,6 @@ static CURL *get_curl_handle(void)
 				 curl_low_speed_time);
 	}
 
-	curl_easy_setopt(result, CURLOPT_FOLLOWLOCATION, 1);
 	curl_easy_setopt(result, CURLOPT_MAXREDIRS, 20);
 #if LIBCURL_VERSION_NUM >= 0x071301
 	curl_easy_setopt(result, CURLOPT_POSTREDIR, CURL_REDIR_POST_ALL);
@@ -734,6 +745,7 @@ static CURL *get_curl_handle(void)
 	if (is_transport_allowed("ftps"))
 		allowed_protocols |= CURLPROTO_FTPS;
 	curl_easy_setopt(result, CURLOPT_REDIR_PROTOCOLS, allowed_protocols);
+	curl_easy_setopt(result, CURLOPT_PROTOCOLS, allowed_protocols);
 #else
 	if (transport_restrict_protocols())
 		warning("protocol restrictions not applied to curl redirects because\n"
@@ -1044,6 +1056,16 @@ struct active_request_slot *get_active_slot(void)
 	curl_easy_setopt(slot->curl, CURLOPT_FAILONERROR, 1);
 	curl_easy_setopt(slot->curl, CURLOPT_RANGE, NULL);
 
+	/*
+	 * Default following to off unless "ALWAYS" is configured; this gives
+	 * callers a sane starting point, and they can tweak for individual
+	 * HTTP_FOLLOW_* cases themselves.
+	 */
+	if (http_follow_config == HTTP_FOLLOW_ALWAYS)
+		curl_easy_setopt(slot->curl, CURLOPT_FOLLOWLOCATION, 1);
+	else
+		curl_easy_setopt(slot->curl, CURLOPT_FOLLOWLOCATION, 0);
+
 #if LIBCURL_VERSION_NUM >= 0x070a08
 	curl_easy_setopt(slot->curl, CURLOPT_IPRESOLVE, git_curl_ipresolve);
 #endif
@@ -1286,9 +1308,12 @@ static int handle_curl_result(struct slot_results *results)
 	 * If we see a failing http code with CURLE_OK, we have turned off
 	 * FAILONERROR (to keep the server's custom error response), and should
 	 * translate the code into failure here.
+	 *
+	 * Likewise, if we see a redirect (30x code), that means we turned off
+	 * redirect-following, and we should treat the result as an error.
 	 */
 	if (results->curl_result == CURLE_OK &&
-	    results->http_code >= 400) {
+	    results->http_code >= 300) {
 		results->curl_result = CURLE_HTTP_RETURNED_ERROR;
 		/*
 		 * Normally curl will already have put the "reason phrase"
@@ -1607,6 +1632,9 @@ static int http_request(const char *url,
 		strbuf_addstr(&buf, " no-cache");
 	if (options && options->keep_error)
 		curl_easy_setopt(slot->curl, CURLOPT_FAILONERROR, 0);
+	if (options && options->initial_request &&
+	    http_follow_config == HTTP_FOLLOW_INITIAL)
+		curl_easy_setopt(slot->curl, CURLOPT_FOLLOWLOCATION, 1);
 
 	headers = curl_slist_append(headers, buf.buf);
 
@@ -1655,16 +1683,16 @@ static int http_request(const char *url,
  *
  * Note that this assumes a sane redirect scheme. It's entirely possible
  * in the example above to end up at a URL that does not even end in
- * "info/refs".  In such a case we simply punt, as there is not much we can
- * do (and such a scheme is unlikely to represent a real git repository,
- * which means we are likely about to abort anyway).
+ * "info/refs".  In such a case we die. There's not much we can do, such a
+ * scheme is unlikely to represent a real git repository, and failing to
+ * rewrite the base opens options for malicious redirects to do funny things.
  */
 static int update_url_from_redirect(struct strbuf *base,
 				    const char *asked,
 				    const struct strbuf *got)
 {
 	const char *tail;
-	size_t tail_len;
+	size_t new_len;
 
 	if (!strcmp(asked, got->buf))
 		return 0;
@@ -1673,14 +1701,16 @@ static int update_url_from_redirect(struct strbuf *base,
 		die("BUG: update_url_from_redirect: %s is not a superset of %s",
 		    asked, base->buf);
 
-	tail_len = strlen(tail);
-
-	if (got->len < tail_len ||
-	    strcmp(tail, got->buf + got->len - tail_len))
-		return 0; /* insane redirect scheme */
+	new_len = got->len;
+	if (!strip_suffix_mem(got->buf, &new_len, tail))
+		die(_("unable to update url base from redirection:\n"
+		      "  asked for: %s\n"
+		      "   redirect: %s"),
+		    asked, got->buf);
 
 	strbuf_reset(base);
-	strbuf_add(base, got->buf, got->len - tail_len);
+	strbuf_add(base, got->buf, new_len);
+
 	return 1;
 }
 

http.h

@@ -116,6 +116,13 @@ extern struct credential http_auth;
 
 extern char curl_errorstr[CURL_ERROR_SIZE];
 
+enum http_follow_config {
+	HTTP_FOLLOW_NONE,
+	HTTP_FOLLOW_ALWAYS,
+	HTTP_FOLLOW_INITIAL
+};
+extern enum http_follow_config http_follow_config;
+
 static inline int missing__target(int code, int result)
 {
 	return	/* file:// URL -- do we ever use one??? */
@@ -139,7 +146,8 @@ extern char *get_remote_object_url(const char *url, const char *hex,
 /* Options for http_get_*() */
 struct http_get_options {
 	unsigned no_cache:1,
-		 keep_error:1;
+		 keep_error:1,
+		 initial_request:1;
 
 	/* If non-NULL, returns the content-type of the response. */
 	struct strbuf *content_type;

remote-curl.c

@@ -274,7 +274,7 @@ static struct discovery *discover_refs(const char *service, int for_push)
 	struct strbuf effective_url = STRBUF_INIT;
 	struct discovery *last = last_discovery;
 	int http_ret, maybe_smart = 0;
-	struct http_get_options options;
+	struct http_get_options http_options;
 
 	if (last && !strcmp(service, last->service))
 		return last;
@@ -291,15 +291,16 @@ static struct discovery *discover_refs(const char *service, int for_push)
 		strbuf_addf(&refs_url, "service=%s", service);
 	}
 
-	memset(&options, 0, sizeof(options));
-	options.content_type = &type;
-	options.charset = &charset;
-	options.effective_url = &effective_url;
-	options.base_url = &url;
-	options.no_cache = 1;
-	options.keep_error = 1;
+	memset(&http_options, 0, sizeof(http_options));
+	http_options.content_type = &type;
+	http_options.charset = &charset;
+	http_options.effective_url = &effective_url;
+	http_options.base_url = &url;
+	http_options.initial_request = 1;
+	http_options.no_cache = 1;
+	http_options.keep_error = 1;
 
-	http_ret = http_get_strbuf(refs_url.buf, &buffer, &options);
+	http_ret = http_get_strbuf(refs_url.buf, &buffer, &http_options);
 	switch (http_ret) {
 	case HTTP_OK:
 		break;
@@ -314,6 +315,9 @@ static struct discovery *discover_refs(const char *service, int for_push)
 		die("unable to access '%s': %s", url.buf, curl_errorstr);
 	}
 
+	if (options.verbosity && !starts_with(refs_url.buf, url.buf))
+		warning(_("redirecting to %s"), url.buf);
+
 	last= xcalloc(1, sizeof(*last_discovery));
 	last->service = service;
 	last->buf_alloc = strbuf_detach(&buffer, &last->len);

t/lib-httpd/apache.conf

@@ -123,6 +123,7 @@ ScriptAlias /error/ error.sh/
 </Files>
 
 RewriteEngine on
+RewriteRule ^/dumb-redir/(.*)$ /dumb/$1 [R=301]
 RewriteRule ^/smart-redir-perm/(.*)$ /smart/$1 [R=301]
 RewriteRule ^/smart-redir-temp/(.*)$ /smart/$1 [R=302]
 RewriteRule ^/smart-redir-auth/(.*)$ /auth/smart/$1 [R=301]
@@ -132,6 +133,19 @@ RewriteRule ^/ftp-redir/(.*)$ ftp://localhost:1000/$1 [R=302]
 RewriteRule ^/loop-redir/x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-x-(.*) /$1 [R=302]
 RewriteRule ^/loop-redir/(.*)$ /loop-redir/x-$1 [R=302]
 
+# The first rule issues a client-side redirect to something
+# that _doesn't_ look like a git repo. The second rule is a
+# server-side rewrite, so that it turns out the odd-looking
+# thing _is_ a git repo. The "[PT]" tells Apache to match
+# the usual ScriptAlias rules for /smart.
+RewriteRule ^/insane-redir/(.*)$ /intern-redir/$1/foo [R=301]
+RewriteRule ^/intern-redir/(.*)/foo$ /smart/$1 [PT]
+
+# Serve info/refs internally without redirecting, but
+# issue a redirect for any object requests.
+RewriteRule ^/redir-objects/(.*/info/refs)$ /dumb/$1 [PT]
+RewriteRule ^/redir-objects/(.*/objects/.*)$ /dumb/$1 [R=301]
+
 # Apache 2.2 does not understand <RequireAll>, so we use RewriteCond.
 # And as RewriteCond does not allow testing for non-matches, we match
 # the desired case first (one has abra, two has cadabra), and let it

t/t5550-http-fetch-dumb.sh

@@ -307,5 +307,66 @@ test_expect_success 'remote-http complains cleanly about malformed urls' '
 	test_must_fail git remote-http http::/example.com/repo.git
 '
 
+test_expect_success 'redirects can be forbidden/allowed' '
+	test_must_fail git -c http.followRedirects=false \
+		clone $HTTPD_URL/dumb-redir/repo.git dumb-redir &&
+	git -c http.followRedirects=true \
+		clone $HTTPD_URL/dumb-redir/repo.git dumb-redir 2>stderr
+'
+
+test_expect_success 'redirects are reported to stderr' '
+	# just look for a snippet of the redirected-to URL
+	test_i18ngrep /dumb/ stderr
+'
+
+test_expect_success 'non-initial redirects can be forbidden' '
+	test_must_fail git -c http.followRedirects=initial \
+		clone $HTTPD_URL/redir-objects/repo.git redir-objects &&
+	git -c http.followRedirects=true \
+		clone $HTTPD_URL/redir-objects/repo.git redir-objects
+'
+
+test_expect_success 'http.followRedirects defaults to "initial"' '
+	test_must_fail git clone $HTTPD_URL/redir-objects/repo.git default
+'
+
+# The goal is for a clone of the "evil" repository, which has no objects
+# itself, to cause the client to fetch objects from the "victim" repository.
+test_expect_success 'set up evil alternates scheme' '
+	victim=$HTTPD_DOCUMENT_ROOT_PATH/victim.git &&
+	git init --bare "$victim" &&
+	git -C "$victim" --work-tree=. commit --allow-empty -m secret &&
+	git -C "$victim" repack -ad &&
+	git -C "$victim" update-server-info &&
+	sha1=$(git -C "$victim" rev-parse HEAD) &&
+
+	evil=$HTTPD_DOCUMENT_ROOT_PATH/evil.git &&
+	git init --bare "$evil" &&
+	# do this by hand to avoid object existence check
+	printf "%s\\t%s\\n" $sha1 refs/heads/master >"$evil/info/refs"
+'
+
+# Here we'll just redirect via HTTP. In a real-world attack these would be on
+# different servers, but we should reject it either way.
+test_expect_success 'http-alternates is a non-initial redirect' '
+	echo "$HTTPD_URL/dumb/victim.git/objects" \
+		>"$evil/objects/info/http-alternates" &&
+	test_must_fail git -c http.followRedirects=initial \
+		clone $HTTPD_URL/dumb/evil.git evil-initial &&
+	git -c http.followRedirects=true \
+		clone $HTTPD_URL/dumb/evil.git evil-initial
+'
+
+# Curl supports a lot of protocols that we'd prefer not to allow
+# http-alternates to use, but it's hard to test whether curl has
+# accessed, say, the SMTP protocol, because we are not running an SMTP server.
+# But we can check that it does not allow access to file://, which would
+# otherwise allow this clone to complete.
+test_expect_success 'http-alternates cannot point at funny protocols' '
+	echo "file://$victim/objects" >"$evil/objects/info/http-alternates" &&
+	test_must_fail git -c http.followRedirects=true \
+		clone "$HTTPD_URL/dumb/evil.git" evil-file
+'
+
 stop_httpd
 test_done

t/t5551-http-fetch-smart.sh

@@ -119,6 +119,10 @@ test_expect_success 'redirects re-root further requests' '
 	git clone $HTTPD_URL/smart-redir-limited/repo.git repo-redir-limited
 '
 
+test_expect_success 're-rooting dies on insane schemes' '
+	test_must_fail git clone $HTTPD_URL/insane-redir/repo.git insane
+'
+
 test_expect_success 'clone from password-protected repository' '
 	echo two >expect &&
 	set_askpass user@host pass@host &&

t/t5812-proto-disable-http.sh

@@ -18,6 +18,7 @@ test_proto "smart http" http "$HTTPD_URL/smart/repo.git"
 
 test_expect_success 'curl redirects respect whitelist' '
 	test_must_fail env GIT_ALLOW_PROTOCOL=http:https \
+			   GIT_SMART_HTTP=0 \
 		git clone "$HTTPD_URL/ftp-redir/repo.git" 2>stderr &&
 	{
 		test_i18ngrep "ftp.*disabled" stderr ||