From afe5d3d516114f08d3c4289682a704f5a7889909 Mon Sep 17 00:00:00 2001
From: Jeff King <peff@peff.net>
Date: Thu, 29 Jan 2009 03:33:02 -0500
Subject: [PATCH] symbolic ref: refuse non-ref targets in HEAD

When calling "git symbolic-ref" it is easy to forget that
the target must be a fully qualified ref. E.g., you might
accidentally do:

  $ git symbolic-ref HEAD master

Unfortunately, this is very difficult to recover from,
because the bogus contents of HEAD make git believe we are
no longer in a git repository (as is_git_dir explicitly
checks for "^refs/heads/" in the HEAD target). So
immediately trying to fix the situation doesn't work:

  $ git symbolic-ref HEAD refs/heads/master
  fatal: Not a git repository

and one is left editing the .git/HEAD file manually.

Furthermore, one might be tempted to use symbolic-ref to set
up a detached HEAD:

  $ git symbolic-ref HEAD `git rev-parse HEAD`

which sets up an even more bogus HEAD:

  $ cat .git/HEAD
  ref: 1a9ace4f2ad4176148e61b5a85cd63d5604aac6d

This patch introduces a small safety valve to prevent the
specific case of anything not starting with refs/heads/ to
go into HEAD. The scope of the safety valve is intentionally
very limited, to make sure that we are not preventing any
behavior that would otherwise be valid (like pointing a
different symref than HEAD outside of refs/heads/).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin-symbolic-ref.c  |  3 +++
 t/t1401-symbolic-ref.sh | 41 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)
 create mode 100755 t/t1401-symbolic-ref.sh

diff --git a/builtin-symbolic-ref.c b/builtin-symbolic-ref.c
index bfc78bb3f..cafc4eba7 100644
--- a/builtin-symbolic-ref.c
+++ b/builtin-symbolic-ref.c
@@ -44,6 +44,9 @@ int cmd_symbolic_ref(int argc, const char **argv, const char *prefix)
 		check_symref(argv[0], quiet);
 		break;
 	case 2:
+		if (!strcmp(argv[0], "HEAD") &&
+		    prefixcmp(argv[1], "refs/heads/"))
+			die("Refusing to point HEAD outside of refs/heads/");
 		create_symref(argv[0], argv[1], msg);
 		break;
 	default:
diff --git a/t/t1401-symbolic-ref.sh b/t/t1401-symbolic-ref.sh
new file mode 100755
index 000000000..569f34177
--- /dev/null
+++ b/t/t1401-symbolic-ref.sh
@@ -0,0 +1,41 @@
+#!/bin/sh
+
+test_description='basic symbolic-ref tests'
+. ./test-lib.sh
+
+# If the tests munging HEAD fail, they can break detection of
+# the git repo, meaning that further tests will operate on
+# the surrounding git repo instead of the trash directory.
+reset_to_sane() {
+	echo ref: refs/heads/foo >.git/HEAD
+}
+
+test_expect_success 'symbolic-ref writes HEAD' '
+	git symbolic-ref HEAD refs/heads/foo &&
+	echo ref: refs/heads/foo >expect &&
+	test_cmp expect .git/HEAD
+'
+
+test_expect_success 'symbolic-ref reads HEAD' '
+	echo refs/heads/foo >expect &&
+	git symbolic-ref HEAD >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'symbolic-ref refuses non-ref for HEAD' '
+	test_must_fail git symbolic-ref HEAD foo
+'
+reset_to_sane
+
+test_expect_success 'symbolic-ref refuses non-branch for HEAD' '
+	test_must_fail git symbolic-ref HEAD refs/foo
+'
+reset_to_sane
+
+test_expect_success 'symbolic-ref refuses bare sha1' '
+	echo content >file && git add file && git commit -m one
+	test_must_fail git symbolic-ref HEAD `git rev-parse HEAD`
+'
+reset_to_sane
+
+test_done
-- 
2.30.2