Re: invalid tree and commit object

From: "René Scharfe" <l.s.r@web.de>
To: Brandon Williams <bwilliamseng@gmail.com>, git <git@vger.kernel.org>
Cc: Jeff King <peff@peff.net>
Subject: Re: invalid tree and commit object
Date: Sat, 9 May 2020 12:16:08 +0200	[thread overview]
Message-ID: <d963242a-72f3-7f42-7c95-ea5148f74804@web.de> (raw)
In-Reply-To: <CALN-EhTpiLERuB16-WPZaLub6GdaRHJW8xDeaOEqSFtKe0kCYw@mail.gmail.com>

Am 09.05.20 um 08:19 schrieb Brandon Williams:
> Here's the setup:
>     tree c63d067eaeed0cbc68b7e4fdf40d267c6b152fe8
>     tree 6241ab2a5314798183b5c4ee8a7b0ccd12c651e6
>     blob 5e1c309dae7f45e0f39b1bf3ac3cd9db12e7d689
>
>     $ git ls-tree c63d067eaeed0cbc68b7e4fdf40d267c6b152fe8
>     100644 blob 5e1c309dae7f45e0f39b1bf3ac3cd9db12e7d689    hello
>     100644 blob 5e1c309dae7f45e0f39b1bf3ac3cd9db12e7d689    hello.c
>     040000 tree 6241ab2a5314798183b5c4ee8a7b0ccd12c651e6    hello

> Am I correct in assuming that this object is indeed invalid and should be
> rejected by fsck?

I'd say yes twice -- what good is a tree that you can't check out because
it contains a d/f conflict?

So I got curious if such trees might be in popular repos, wrote the patch
below and checked around a bit, but couldn't find any.

Is there a smarter way to check for duplicates?  One that doesn't need
allocations?  Perhaps by having a version of tree_entry_extract() that
seeks backwards somehow?

---
 fsck.c          | 10 ++++++++++
 t/t1450-fsck.sh | 16 ++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/fsck.c b/fsck.c
index 087a7f1ffc..f47b35fee8 100644
--- a/fsck.c
+++ b/fsck.c
@@ -587,6 +587,8 @@ static int fsck_tree(const struct object_id *oid,
 	struct tree_desc desc;
 	unsigned o_mode;
 	const char *o_name;
+	struct string_list names = STRING_LIST_INIT_NODUP;
+	size_t nr;

 	if (init_tree_desc_gently(&desc, buffer, size)) {
 		retval += report(options, oid, OBJ_TREE, FSCK_MSG_BAD_TREE, "cannot be parsed as a tree");
@@ -680,8 +682,16 @@ static int fsck_tree(const struct object_id *oid,

 		o_mode = mode;
 		o_name = name;
+		string_list_append(&names, name);
 	}

+	nr = names.nr;
+	string_list_sort(&names);
+	string_list_remove_duplicates(&names, 0);
+	if (names.nr != nr)
+		has_dup_entries = 1;
+	string_list_clear(&names, 0);
+
 	if (has_null_sha1)
 		retval += report(options, oid, OBJ_TREE, FSCK_MSG_NULL_SHA1, "contains entries pointing to null sha1");
 	if (has_full_path)
diff --git a/t/t1450-fsck.sh b/t/t1450-fsck.sh
index 449ebc5657..91a6e34f38 100755
--- a/t/t1450-fsck.sh
+++ b/t/t1450-fsck.sh
@@ -257,6 +257,22 @@ test_expect_success 'tree object with duplicate entries' '
 	test_i18ngrep "error in tree .*contains duplicate file entries" out
 '

+test_expect_success 'tree object with dublicate names' '
+	test_when_finished "remove_object \$blob" &&
+	test_when_finished "remove_object \$tree" &&
+	test_when_finished "remove_object \$badtree" &&
+	blob=$(echo blob | git hash-object -w --stdin) &&
+	printf "100644 blob %s\t%s\n" $blob x.2 >tree &&
+	tree=$(git mktree <tree) &&
+	printf "100644 blob %s\t%s\n" $blob x.1 >badtree &&
+	printf "100644 blob %s\t%s\n" $blob x >>badtree &&
+	printf "040000 tree %s\t%s\n" $tree x >>badtree &&
+	badtree=$(git mktree <badtree) &&
+	test_must_fail git fsck 2>out &&
+	test_i18ngrep "$badtree" out &&
+	test_i18ngrep "error in tree .*contains duplicate file entries" out
+'
+
 test_expect_success 'unparseable tree object' '
 	test_oid_cache <<-\EOF &&
 	junk sha1:twenty-bytes-of-junk
--
2.26.2
