Git.pm: trust rev-parse to find bare repositories

When initializing a repository object, we run "git rev-parse --git-dir"
to let the C version of Git find the correct directory. But curiously,
if this fails we don't automatically say "not a git repository".
Instead, we do our own pure-perl check to see if we're in a bare
repository.

This makes little sense, as rev-parse will report both bare and non-bare
directories. This logic comes from d5c7721d58 (Git.pm: Add support for
subdirectories inside of working copies, 2006-06-24), but I don't see
any reason given why we can't just rely on rev-parse. Worse, because we
treat any non-error response from rev-parse as a non-bare repository,
we'll erroneously set the object's WorkingCopy, even in a bare
repository.

But it gets worse. Since 8959555cee (setup_git_directory(): add an owner
check for the top-level directory, 2022-03-02), it's actively wrong (and
dangerous). The perl code doesn't implement the same ownership checks.
And worse, after "finding" the bare repository, it sets GIT_DIR in the
environment, which tells any subsequent Git commands that we've
confirmed the directory is OK, and to trust us. I.e., it re-opens the
vulnerability plugged by 8959555cee when using Git.pm's repository
discovery code.

We can fix this by just relying on rev-parse to tell us when we're not
in a repository, which fixes the vulnerability. Furthermore, we'll ask
its --is-bare-repository function to tell us if we're bare or not, and
rely on that.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 32 insertions, 20 deletions

diff --git a/perl/Git.pm b/perl/Git.pm
index cf15ead664..117765dc73 100644
--- a/perl/Git.pm
+++ b/perl/Git.pm
@@ -177,16 +177,27 @@ sub repository {
 		-d $opts{Directory} or throw Error::Simple("Directory not found: $opts{Directory} $!");
 
 		my $search = Git->repository(WorkingCopy => $opts{Directory});
-		my $dir;
+
+		# This rev-parse will throw an exception if we're not in a
+		# repository, which is what we want, but it's kind of noisy.
+		# Ideally we'd capture stderr and relay it, but doing so is
+		# awkward without depending on it fitting in a pipe buffer. So
+		# we just reproduce a plausible error message ourselves.
+		my $out;
 		try {
-			$dir = $search->command_oneline(['rev-parse', '--git-dir'],
-			                                STDERR => 0);
+		  # Note that "--is-bare-repository" must come first, as
+		  # --git-dir output could contain newlines.
+		  $out = $search->command([qw(rev-parse --is-bare-repository --git-dir)],
+			                  STDERR => 0);
 		} catch Git::Error::Command with {
-			$dir = undef;
+			throw Error::Simple("fatal: not a git repository: $opts{Directory}");
 		};
 
+		chomp $out;
+		my ($bare, $dir) = split /\n/, $out, 2;
+
 		require Cwd;
-		if ($dir) {
+		if ($bare ne 'true') {
 			require File::Spec;
 			File::Spec->file_name_is_absolute($dir) or $dir = $opts{Directory} . '/' . $dir;
 			$opts{Repository} = Cwd::abs_path($dir);
@@ -204,21 +215,6 @@ sub repository {
 			$opts{WorkingSubdir} = $prefix;
 
 		} else {
-			# A bare repository? Let's see...
-			$dir = $opts{Directory};
-
-			unless (-d "$dir/refs" and -d "$dir/objects" and -e "$dir/HEAD") {
-				# Mimic git-rev-parse --git-dir error message:
-				throw Error::Simple("fatal: Not a git repository: $dir");
-			}
-			my $search = Git->repository(Repository => $dir);
-			try {
-				$search->command('symbolic-ref', 'HEAD');
-			} catch Git::Error::Command with {
-				# Mimic git-rev-parse --git-dir error message:
-				throw Error::Simple("fatal: Not a git repository: $dir");
-			};
-
 			$opts{Repository} = Cwd::abs_path($dir);
 		}
 
diff --git a/t/t9700-perl-git.sh b/t/t9700-perl-git.sh
index 4aa5d90d32..b105d6d9d5 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 e046f7db76..6d753708d2 100755
--- a/t/t9700/test.pl
+++ b/t/t9700/test.pl
@@ -30,6 +30,18 @@ BEGIN { use_ok('Git') }
 # set up
 our $abs_repo_dir = cwd();
 ok(our $r = Git->repository(Directory => "."), "open repository");
+{
+	local $ENV{GIT_TEST_ASSUME_DIFFERENT_OWNER} = 1;
+	my $failed;
+
+	$failed = eval { Git->repository(Directory => $abs_repo_dir) };
+	ok(!$failed, "reject unsafe non-bare repository");
+	like($@, qr/not a git repository/i, "unsafe error message");
+
+	$failed = eval { Git->repository(Directory => "$abs_repo_dir/bare.git") };
+	ok(!$failed, "reject unsafe bare repository");
+	like($@, qr/not a git repository/i, "unsafe error message");
+}
 
 # config
 is($r->config("test.string"), "value", "config scalar: string");