hooks(clone protections): special-case current Git LFS hooks

A notable regression in v2.45.1 and friends (all the way down to
v2.39.4) has been that Git LFS-enabled clones error out with a message
indicating that the `post-checkout` hook has been tampered with while
cloning, and as a safety measure it is not executed.

A generic fix for benign third-party applications wishing to write hooks
during clone operations has been implemented in the parent of this
commit: said applications are expected to add `safe.hook.sha256` values
to a protected config.

However, the current version of Git LFS, v3.5.1, cannot be adapted
retroactively; Therefore, let's just hard-code the SHA-256 values for
this version. That way, Git LFS usage will no longer be broken, and the
next Git LFS version can be taught to add those `safe.hook.sha256`
entries.

Signed-off-by: Johannes Schindelin <[email protected]>

hook.c

@@ -77,6 +77,17 @@ static int is_hook_safe_during_clone(const char *name, const char *path, char *s
 
 	if (!safe_hook_sha256s_initialized) {
 		safe_hook_sha256s_initialized = 1;
+
+		/* Hard-code known-safe values for Git LFS v3.4.0..v3.5.1 */
+		/* pre-push */
+		strset_add(&safe_hook_sha256s, "df5417b2daa3aa144c19681d1e997df7ebfe144fb7e3e05138bd80ae998008e4");
+		/* post-checkout */
+		strset_add(&safe_hook_sha256s, "791471b4ff472aab844a4fceaa48bbb0a12193616f971e8e940625498b4938a6");
+		/* post-commit */
+		strset_add(&safe_hook_sha256s, "21e961572bb3f43a5f2fbafc1cc764d86046cc2e5f0bbecebfe9684a0b73b664");
+		/* post-merge */
+		strset_add(&safe_hook_sha256s, "75da0da66a803b4b030ad50801ba57062c6196105eb1d2251590d100edb9390b");
+
 		git_protected_config(safe_hook_cb, &safe_hook_sha256s);
 	}
 

t/t1800-hook.sh

@@ -192,4 +192,24 @@ test_expect_success '`safe.hook.sha256` and clone protections' '
 	test "called hook" = "$(cat safe-hook/safe-hook.log)"
 '
 
+write_lfs_pre_push_hook () {
+	write_script "$1" <<-\EOF
+	command -v git-lfs >/dev/null 2>&1 || { echo >&2 "\nThis repository is configured for Git LFS but 'git-lfs' was not found on your path. If you no longer wish to use Git LFS, remove this hook by deleting the 'pre-push' file in the hooks directory (set by 'core.hookspath'; usually '.git/hooks').\n"; exit 2; }
+	git lfs pre-push "$@"
+	EOF
+}
+
+test_expect_success 'Git LFS special-handling in clone protections' '
+	git init lfs-hooks &&
+	write_lfs_pre_push_hook lfs-hooks/.git/hooks/pre-push &&
+	write_script git-lfs <<-\EOF &&
+	echo "called $*" >fake-git-lfs.log
+	EOF
+
+	PATH="$PWD:$PATH" GIT_CLONE_PROTECTION_ACTIVE=true \
+		git -C lfs-hooks hook run pre-push &&
+	test_write_lines "called pre-push" >expect &&
+	test_cmp lfs-hooks/fake-git-lfs.log expect
+'
+
 test_done