From 935af59cf64fbe49eb8baba9fe80e6b236daf593 Mon Sep 17 00:00:00 2001
From: Christian Muehlhaeuser <muesli@gmail.com>
Date: Wed, 19 Jan 2022 15:51:13 +0100
Subject: [PATCH] Repository: don't crash accessing invalid pathinfo (#443)

When fs.Stat returns an error, pathinfo may be nil. In such situations
the only safe response seems to be to return the error to the caller.

Without this fix, accessing pathinfo.IsDir() below would lead to a crash
dereferencing a nil pointer.

This crash can be reproduced by trying to initialize a Git repo with an
invalid path name.

Also see: https://github.com/muesli/gitty/issues/36
---
 repository.go      | 3 +++
 repository_test.go | 5 +++++
 2 files changed, 8 insertions(+)

diff --git a/repository.go b/repository.go
index e8eb53f70..7292df627 100644
--- a/repository.go
+++ b/repository.go
@@ -280,6 +280,9 @@ func dotGitToOSFilesystems(path string, detect bool) (dot, wt billy.Filesystem,
 
 		pathinfo, err := fs.Stat("/")
 		if !os.IsNotExist(err) {
+			if pathinfo == nil {
+				return nil, nil, err
+			}
 			if !pathinfo.IsDir() && detect {
 				fs = osfs.New(filepath.Dir(path))
 			}
diff --git a/repository_test.go b/repository_test.go
index e284df8d6..7a9db151d 100644
--- a/repository_test.go
+++ b/repository_test.go
@@ -2948,6 +2948,11 @@ func (s *RepositorySuite) TestBrokenMultipleShallowFetch(c *C) {
 	c.Assert(err, IsNil)
 }
 
+func (s *RepositorySuite) TestDotGitToOSFilesystemsInvalidPath(c *C) {
+	_, _, err := dotGitToOSFilesystems("\000", false)
+	c.Assert(err, NotNil)
+}
+
 func BenchmarkObjects(b *testing.B) {
 	defer fixtures.Clean()