fsck: detect gitmodules URLs with embedded newlines

The credential protocol can't handle values with newlines. We already
detect and block any such URLs from being used with credential helpers,
but let's also add an fsck check to detect and block gitmodules files
with such URLs. That will let us notice the problem earlier when
transfer.fsckObjects is turned on. And in particular it will prevent bad
objects from spreading, which may protect downstream users running older
versions of Git.

We'll file this under the existing gitmodulesUrl flag, which covers URLs
with option injection. There's really no need to distinguish the exact
flaw in the URL in this context. Likewise, I've expanded the description
of t7416 to cover all types of bogus URLs.

1 files changed, 15 insertions, 1 deletions

diff --git a/fsck.c b/fsck.c
index 0741e62586..5b437c260c 100644
--- a/fsck.c
+++ b/fsck.c
@@ -14,6 +14,7 @@
 #include "packfile.h"
 #include "submodule-config.h"
 #include "config.h"
+#include "credential.h"
 
 static struct oidset gitmodules_found = OIDSET_INIT;
 static struct oidset gitmodules_done = OIDSET_INIT;
@@ -941,6 +942,19 @@ static int fsck_tag(struct tag *tag, const char *data,
 	return fsck_tag_buffer(tag, data, size, options);
 }
 
+static int check_submodule_url(const char *url)
+{
+	struct credential c = CREDENTIAL_INIT;
+	int ret;
+
+	if (looks_like_command_line_option(url))
+		return -1;
+
+	ret = credential_from_url_gently(&c, url, 1);
+	credential_clear(&c);
+	return ret;
+}
+
 struct fsck_gitmodules_data {
 	struct object *obj;
 	struct fsck_options *options;
@@ -965,7 +979,7 @@ static int fsck_gitmodules_fn(const char *var, const char *value, void *vdata)
 				    "disallowed submodule name: %s",
 				    name);
 	if (!strcmp(key, "url") && value &&
-	    looks_like_command_line_option(value))
+	    check_submodule_url(value) < 0)
 		data->ret |= report(data->options, data->obj,
 				    FSCK_MSG_GITMODULES_URL,
 				    "disallowed submodule url: %s",