[PATCH] archive-tar: fix sanity check in config parsing

git archive supports passing generated tar archives through filter
commands like gzip.  Additional filters can be set up using the
configuration variables tar.<name>.command and tar.<name>.remote.

When parsing these config variable names, we currently check that
the second dot is found nine characters into the name, disallowing
filter names with a length of five characters.  Additionally,
git archive crashes when the second dot is omitted:

	$ ./git -c tar.foo=bar archive HEAD >/dev/null
	fatal: Data too large to fit into virtual memory space.

Instead we should check if the second dot exists at all, or if
we only found the first one.

Signed-off-by: Rene Scharfe <redacted>
---
 archive-tar.c       | 2 +-
 t/t5000-tar-tree.sh | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/archive-tar.c b/archive-tar.c
index d1cce46..093d10e 100644
--- a/archive-tar.c
+++ b/archive-tar.c

@@ -335,7 +335,7 @@ static int tar_filter_config(const char *var, const char *value, void *data)
 	if (prefixcmp(var, "tar."))
 		return 0;
 	dot = strrchr(var, '.');
-	if (dot == var + 9)
+	if (dot == var + 3)
 		return 0;
 
 	name = var + 4;

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 'git-archive --prefix=olde-' '
 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