[PATCHv2 2/8] archive-tar: use parse_config_key when parsing config

[Jeff King <peff@peff.net>]

This is fewer lines of code, but more importantly, fixes a
bogus pointer offset. We are looking for "tar." in the
section, but later assume that the dot we found is at offset
9, not 3. This is a holdover from an earlier iteration of
767cf45 which called the section "tarfilter".

As a result, we could erroneously reject some filters with
dots in their name, as well as read uninitialized memory.

Reported by (and test by) René Scharfe.

Signed-off-by: Jeff King <peff@peff.net>
---
 archive-tar.c       | 10 +---------
 t/t5000-tar-tree.sh |  3 ++-
 2 files changed, 3 insertions(+), 10 deletions(-)

diff --git a/archive-tar.c b/archive-tar.c
index d1cce46..719b629 100644
--- a/archive-tar.c
+++ b/archive-tar.c
@@ -327,20 +327,12 @@ static int tar_filter_config(const char *var, const char *value, void *data)
 static int tar_filter_config(const char *var, const char *value, void *data)
 {
 	struct archiver *ar;
-	const char *dot;
 	const char *name;
 	const char *type;
 	int namelen;
 
-	if (prefixcmp(var, "tar."))
+	if (parse_config_key(var, "tar", &name, &namelen, &type) < 0 || !name)
 		return 0;
-	dot = strrchr(var, '.');
-	if (dot == var + 9)
-		return 0;
-
-	name = var + 4;
-	namelen = dot - name;
-	type = dot + 1;
 
 	ar = find_tar_filter(name, namelen);
 	if (!ar) {
diff --git a/t/t5000-tar-tree.sh b/t/t5000-tar-tree.sh
index e7c240f..3fbd366 100755
--- a/t/t5000-tar-tree.sh
+++ b/t/t5000-tar-tree.sh
@@ -212,7 +212,8 @@ test_expect_success 'setup tar filters' '
 test_expect_success 'setup tar filters' '
 	git config tar.tar.foo.command "tr ab ba" &&
 	git config tar.bar.command "tr ab ba" &&
-	git config tar.bar.remote true
+	git config tar.bar.remote true &&
+	git config tar.invalid baz
 '
 
 test_expect_success 'archive --list mentions user filter' '
-- 
1.8.0.2.15.g815dc66