[PATCH v2 2/2] setup: allow Git.pm to do unsafe repo checking

From: Michael McClimon <michael@mcclimon.org>
Date: Oct 22, 2022, 01:19 UTC
Message-ID: <20221022011931.43992-3-michael@mcclimon.org>
In-Reply-To: <20221022011931.43992-1-michael@mcclimon.org>

The previous commit exposes a security flaw: it is possible to bypass unsafe repository checks by using Git.pm, where before the syntax error accidentally prohibited it. This problem occurs because Git.pm sets GIT_DIR explicitly, which bypasses the safe repository checks.

Fix this by introducing a new environment variable, GIT_PERL_FORCE_OWNERSHIP_CHECK, which we set true in Git.pm. In setup.c, if that environment variable is true, force ownership checks even if an explicit GIT_DIR is provided.

Signed-off-by: Michael McClimon <michael@mcclimon.org>
---
 perl/Git.pm         |  1 +
 setup.c             |  3 +++
 t/t9700-perl-git.sh |  4 ++++
 t/t9700/test.pl     | 18 ++++++++++++++++++
 4 files changed, 26 insertions(+)

diff --git a/perl/Git.pm b/perl/Git.pm
index cf15ead6..002c29bb 100644
--- a/perl/Git.pm
+++ b/perl/Git.pm
@@ -1674,6 +1674,7 @@ sub _cmd_exec {
 sub _setup_git_cmd_env {
 	my $self = shift;
 	if ($self) {
+		$ENV{GIT_PERL_FORCE_OWNERSHIP_CHECK} = 1;
 		$self->repo_path() and $ENV{'GIT_DIR'} = $self->repo_path();
 		$self->repo_path() and $self->wc_path()
 			and $ENV{'GIT_WORK_TREE'} = $self->wc_path();
diff --git a/setup.c b/setup.c
index cefd5f63..33d4e6fd 100644
--- a/setup.c
+++ b/setup.c
@@ -1250,6 +1250,9 @@ static enum discovery_result setup_git_directory_gently_1(struct strbuf *dir,
 	 */
 	gitdirenv = getenv(GIT_DIR_ENVIRONMENT);
 	if (gitdirenv) {
+		if (git_env_bool("GIT_PERL_FORCE_OWNERSHIP_CHECK", 0) &&
+		    !ensure_valid_ownership(NULL, NULL, gitdirenv, report))
+			return GIT_DIR_INVALID_OWNERSHIP;
 		strbuf_addstr(gitdir, gitdirenv);
 		return GIT_DIR_EXPLICIT;
 	}
diff --git a/t/t9700-perl-git.sh b/t/t9700-perl-git.sh
index 4aa5d90d..b14a40b1 100755
--- a/t/t9700-perl-git.sh
+++ b/t/t9700-perl-git.sh
@@ -45,6 +45,10 @@ test_expect_success \
      git config --add test.pathmulti bar
      '
 
+test_expect_success 'set up bare repository' '
+     git init --bare bare.git
+'
+
 test_expect_success 'use t9700/test.pl to test Git.pm' '
 	"$PERL_PATH" "$TEST_DIRECTORY"/t9700/test.pl 2>stderr &&
 	test_must_be_empty stderr
diff --git a/t/t9700/test.pl b/t/t9700/test.pl
index e046f7db..1c91019f 100755
--- a/t/t9700/test.pl
+++ b/t/t9700/test.pl
@@ -142,6 +142,24 @@ sub adjust_dirsep {
 		     "abc\"\\ \x07\x08\x09\x0a\x0b\x0c\x0d\x01 ",
 		     'unquote escape sequences');
 
+# safe directory
+{
+	local $ENV{GIT_TEST_ASSUME_DIFFERENT_OWNER} = 1;
+	# Save stderr to a tempfile so we can check the contents
+	open our $tmpstderr2, ">&STDERR" or die "cannot save STDERR";
+	my $tmperr = "unsafeerr.tmp";
+	open STDERR, ">", "$tmperr" or die "cannot redirect STDERR to $tmperr";
+	my $failed = eval { Git->repository(Directory => "$abs_repo_dir/bare.git") };
+	ok(!$failed, "reject unsafe repository");
+	like($@, qr/not a git repository/i, "unsafe error message");
+	open TEMPFILE, "<", "$tmperr" or die "Can't open $tmperr $!";
+	my $errcontents;
+	{ local $/; $errcontents = <TEMPFILE>; }
+	like($errcontents, qr/dubious ownership/, "dubious ownership message");
+	close STDERR or die "cannot close temp stderr";
+	open STDERR, ">&", $tmpstderr2 or die "cannot restore STDERR";
+}
+
 printf "1..%d\n", Test::More->builder->current_test;
 
 my $is_passing = eval { Test::More->is_passing };

-- 
2.38.1.130.g45c9f05c