refs: check refnames as fully qualified when writing

When a ref update is queued via ref_transaction_update(), we call
check_refname_format() to make sure the name is acceptable. We pass
REFNAME_ALLOW_ONELEVEL, which allows pseudorefs like MERGE_HEAD. But
that's not enough to forbid names outside of refs/ like "foo/bar" or
even scary stuff like "config" (though fortunately I think that should
never work because we cannot resolve "config" to read the old value).

Let's instead pass REFNAME_FULLY_QUALIFIED, which tells the checking
function that we really do have a full refname, and it can enforce
it as such.

This means that "git update-ref foo/bar HEAD" will now be rejected. Note
that _deleting_ such a ref is already forbidden (and there is a test in
t1430 for that already), due to some confusing differences between
check_refname_format() and refname_is_safe(). See the previous commit
for more details. And that case is already tested via t1430's
"update-ref -d cannot delete non-ref in .git dir" test, so we only need
to add tests for our newly-changed behavior.

Signed-off-by: Jeff King <peff@peff.net>

Author: peff

refs.c

@@ -1381,7 +1381,7 @@ static int transaction_refname_valid(const char *refname,
 		strbuf_addf(err, refusal_msg, refname);
 		return 0;
 	} else if ((new_oid && !is_null_oid(new_oid)) ?
-		 check_refname_format(refname, REFNAME_ALLOW_ONELEVEL) :
+		 check_refname_format(refname, REFNAME_FULLY_QUALIFIED) :
 		 !refname_is_safe(refname)) {
 		const char *refusal_msg;
 		if (flags & REF_LOG_ONLY)

t/t1430-bad-ref-name.sh

@@ -389,4 +389,14 @@ test_expect_success 'branch -m can rename refs/heads/-dash' '
 	git show-ref refs/heads/dash
 '
 
+test_expect_success 'update-ref refuses lowercase outside of refs/' '
+	test_must_fail git update-ref lowercase HEAD 2>err &&
+	test_grep "refusing to update ref with bad name" err
+'
+
+test_expect_success 'update-ref refuses non-underscore punctuation outside of refs/' '
+	test_must_fail git update-ref FOO/HEAD HEAD 2>err &&
+	test_grep "refusing to update ref with bad name" err
+'
+
 test_done