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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>
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1 parent b229d18 commit afe5d3d516114f08d3c4289682a704f5a7889909 @peff peff committed with gitster Jan 29, 2009
Showing with 44 additions and 0 deletions.
  1. +3 −0 builtin-symbolic-ref.c
  2. +41 −0 t/t1401-symbolic-ref.sh
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@@ -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:
View
@@ -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

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