fsck: detect submodule urls starting with dash

Urls with leading dashes can cause mischief on older
versions of Git. We should detect them so that they can be
rejected by receive.fsckObjects, preventing modern versions
of git from being a vector by which attacks can spread.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

fsck.c

diff --git a/fsck.c b/fsck.c
index 9339f31..c472856 100644
--- a/fsck.c
+++ b/fsck.c
@@ -64,6 +64,7 @@ static struct oidset gitmodules_done = OIDSET_INIT;
 	FUNC(GITMODULES_PARSE, ERROR) \
 	FUNC(GITMODULES_NAME, ERROR) \
 	FUNC(GITMODULES_SYMLINK, ERROR) \
+	FUNC(GITMODULES_URL, ERROR) \
 	/* warnings */ \
 	FUNC(BAD_FILEMODE, WARN) \
 	FUNC(EMPTY_NAME, WARN) \
@@ -945,6 +946,12 @@ static int fsck_gitmodules_fn(const char *var, const char *value, void *vdata)
 				    FSCK_MSG_GITMODULES_NAME,
 				    "disallowed submodule name: %s",
 				    name);
+	if (!strcmp(key, "url") && value &&
+	    looks_like_command_line_option(value))
+		data->ret |= report(data->options, data->obj,
+				    FSCK_MSG_GITMODULES_URL,
+				    "disallowed submodule url: %s",
+				    value);
 	free(name);
 
 	return 0;

t/t7416-submodule-dash-url.sh

diff --git a/t/t7416-submodule-dash-url.sh b/t/t7416-submodule-dash-url.sh
index 459193c..1cd2c1c 100755
--- a/t/t7416-submodule-dash-url.sh
+++ b/t/t7416-submodule-dash-url.sh
@@ -20,6 +20,13 @@
 	test_cmp expect actual
 '
 
+test_expect_success 'fsck accepts protected dash' '
+	test_when_finished "rm -rf dst" &&
+	git init --bare dst &&
+	git -C dst config transfer.fsckObjects true &&
+	git push dst HEAD
+'
+
 test_expect_success 'remove ./ protection from .gitmodules url' '
 	perl -i -pe "s{\./}{}" .gitmodules &&
 	git commit -am "drop protection"
@@ -31,4 +38,12 @@
 	test_i18ngrep ignoring err
 '
 
+test_expect_success 'fsck rejects unprotected dash' '
+	test_when_finished "rm -rf dst" &&
+	git init --bare dst &&
+	git -C dst config transfer.fsckObjects true &&
+	test_must_fail git push dst HEAD 2>err &&
+	grep gitmodulesUrl err
+'
+
 test_done