diff mbox series

[v4,04/39] t3404: prepare 'short SHA-1 collision' tests for SHA-256

Message ID 20200726195424.626969-5-sandals@crustytoothpaste.net (mailing list archive)
State New, archived
Headers show
Series [v4,01/39] t: make test-bloom initialize repository | expand

Commit Message

brian m. carlson July 26, 2020, 7:53 p.m. UTC 
From: Johannes Schindelin <johannes.schindelin@gmx.de>

The idea of the magic value "ac4f2ee" in this test is to make the
reworded commit `collide2` have the same shortened ID as the commit
`collide3`.

To port the same idea to the SHA-256 version of Git, we therefore need
another magic value that causes the same collision, but this time with
the SHA-256 version of the commit IDs.

In this patch, we add code guarded by `GIT_TEST_FIND_COLLIDER` to do
exactly that. Essentially, a large number of integers is appended to the
commit message "collide2" to find such a collision. To make it easier to
find such a collision, we reduce the number of digits to 4.

The `t/oid-info/oid` file now lists the values found in that way, and
the test cases are modified to use those values.

As the tests are no longer dependent on SHA-1, we also rename their
titles to talk about "commit IDs" instead of "SHA-1s".

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
---
 t/t3404-rebase-interactive.sh | 50 ++++++++++++++++++++++++++++-------
 1 file changed, 41 insertions(+), 9 deletions(-)

Comments

Eric Sunshine July 26, 2020, 10:31 p.m. UTC | #1 
On Sun, Jul 26, 2020 at 3:55 PM brian m. carlson
<sandals@crustytoothpaste.net> wrote:
> The idea of the magic value "ac4f2ee" in this test is to make the
> reworded commit `collide2` have the same shortened ID as the commit
> `collide3`.
>
> To port the same idea to the SHA-256 version of Git, we therefore need
> another magic value that causes the same collision, but this time with
> the SHA-256 version of the commit IDs.
>
> In this patch, we add code guarded by `GIT_TEST_FIND_COLLIDER` to do
> exactly that. Essentially, a large number of integers is appended to the
> commit message "collide2" to find such a collision. To make it easier to
> find such a collision, we reduce the number of digits to 4.
>
> The `t/oid-info/oid` file now lists the values found in that way, and
> the test cases are modified to use those values.

This seems to be saying that t/oid-info/oid has been updated to
contain the colliding OID's generated for this test, however, those
OID's are actually specified inline in the test itself (which is the
appropriate place for them since they are specific to this test). So,
this paragraph/sentence probably ought to be dropped.

> As the tests are no longer dependent on SHA-1, we also rename their
> titles to talk about "commit IDs" instead of "SHA-1s".
>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
> ---
> diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
> @@ -1262,23 +1263,54 @@ test_expect_success SHA1 'short SHA-1 setup' '
> +test_expect_success 'short commit ID collide' '
> +       test_oid_cache <<-EOF &&
> +       # collision-related constants
> +       t3404_collision sha1:6bcd
> +       t3404_collision sha256:0161
> +       t3404_collider  sha1:ac4f2ee
> +       t3404_collider  sha256:16697
> +       EOF
diff mbox series

Patch

diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 4a7d21f898..2fb2c581cb 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -30,6 +30,7 @@  Initial setup:
 . "$TEST_DIRECTORY"/lib-rebase.sh
 
 test_expect_success 'setup' '
+	test_oid_init &&
 	test_commit A file1 &&
 	test_commit B file1 &&
 	test_commit C file2 &&
@@ -1250,7 +1251,7 @@  test_expect_success 'rebase -i error on commits with \ in message' '
 	test_expect_code 1 grep  "	emp" error
 '
 
-test_expect_success SHA1 'short SHA-1 setup' '
+test_expect_success 'short commit ID setup' '
 	test_when_finished "git checkout master" &&
 	git checkout --orphan collide &&
 	git rm -rf . &&
@@ -1262,23 +1263,54 @@  test_expect_success SHA1 'short SHA-1 setup' '
 	)
 '
 
-test_expect_success SHA1 'short SHA-1 collide' '
+if test -n "$GIT_TEST_FIND_COLLIDER"
+then
+	author="$(unset test_tick; test_tick; git var GIT_AUTHOR_IDENT)"
+	committer="$(unset test_tick; test_tick; git var GIT_COMMITTER_IDENT)"
+	blob="$(git rev-parse collide2:collide)"
+	from="$(git rev-parse collide1^0)"
+	repl="commit refs/heads/collider-&\\n"
+	repl="${repl}author $author\\ncommitter $committer\\n"
+	repl="${repl}data <<EOF\\ncollide2 &\\nEOF\\n"
+	repl="${repl}from $from\\nM 100644 $blob collide\\n"
+	test_seq 1 32768 | sed "s|.*|$repl|" >script &&
+	git fast-import <script &&
+	git pack-refs &&
+	git for-each-ref >refs &&
+	grep "^$(test_oid t3404_collision)" <refs >matches &&
+	cat matches &&
+	test_line_count -gt 2 matches || {
+		echo "Could not find a collider" >&2
+		exit 1
+	}
+fi
+
+test_expect_success 'short commit ID collide' '
+	test_oid_cache <<-EOF &&
+	# collision-related constants
+	t3404_collision	sha1:6bcd
+	t3404_collision	sha256:0161
+	t3404_collider	sha1:ac4f2ee
+	t3404_collider	sha256:16697
+	EOF
 	test_when_finished "reset_rebase && git checkout master" &&
 	git checkout collide &&
-	colliding_sha1=6bcda37 &&
-	test $colliding_sha1 = "$(git rev-parse HEAD | cut -c 1-7)" &&
+	colliding_id=$(test_oid t3404_collision) &&
+	hexsz=$(test_oid hexsz) &&
+	test $colliding_id = "$(git rev-parse HEAD | cut -c 1-4)" &&
+	test_config core.abbrev 4 &&
 	(
 		unset test_tick &&
 		test_tick &&
 		set_fake_editor &&
-		FAKE_COMMIT_MESSAGE="collide2 ac4f2ee" \
+		FAKE_COMMIT_MESSAGE="collide2 $(test_oid t3404_collider)" \
 		FAKE_LINES="reword 1 break 2" git rebase -i HEAD~2 &&
-		test $colliding_sha1 = "$(git rev-parse HEAD | cut -c 1-7)" &&
-		grep "^pick $colliding_sha1 " \
+		test $colliding_id = "$(git rev-parse HEAD | cut -c 1-4)" &&
+		grep "^pick $colliding_id " \
 			.git/rebase-merge/git-rebase-todo.tmp &&
-		grep "^pick [0-9a-f]\{40\}" \
+		grep "^pick [0-9a-f]\{$hexsz\}" \
 			.git/rebase-merge/git-rebase-todo &&
-		grep "^pick [0-9a-f]\{40\}" \
+		grep "^pick [0-9a-f]\{$hexsz\}" \
 			.git/rebase-merge/git-rebase-todo.backup &&
 		git rebase --continue
 	) &&