From da790954174859dff0827015e48559b3df865ae3 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 1afe0b27a..0049f1d05 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 a80346eff..8f2e36a65 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()