Backport fix from #497 to v2 (#498)

* Recreate git config during update to prevent git config alteration

Backport fix from #497 to v2

* Bump version of Golang container to match module version

The Go module for v2 is 1.19, bumping the base docker image to match the
minimum version ensures go-getter can be compiled and executed on the
container. This change resolves the failing acceptance test for Samba.

```
Run docker exec -i gogetter bash -c "env ACC_SMB_TEST=1 go test -v ./... -run=TestSmb_"
  docker exec -i gogetter bash -c "env ACC_SMB_TEST=1 go test -v ./... -run=TestSmb_"
  shell: /usr/bin/bash -e {0}
  env:
    TEST_RESULTS_PATH: /tmp/test-results
Error: ./get_git.go:366:16: undefined: os.ReadDir
Error: ./get_git_test.go:886:9: undefined: os.WriteFile
Error: ./get_git_test.go:904:22: undefined: os.ReadFile
note: module requires Go 1.19
FAIL	github.com/hashicorp/go-getter/v2 [build failed]
?   	github.com/hashicorp/go-getter/v2/helper/testing	[no test files]
testing: warning: no tests to run
PASS
ok  	github.com/hashicorp/go-getter/v2/helper/url	0.006s [no tests to run]
FAIL
Error: Process completed with exit code 2.

```

Dockerfile

@@ -1,5 +1,5 @@
 # Dockerfile to create a go-getter container with smbclient dependency that is used by the get_smb.go tests
-FROM golang:1.15
+FROM golang:1.19.13
 
 COPY . /go-getter
 WORKDIR /go-getter

get_git.go

@@ -122,7 +122,7 @@ func (g *GitGetter) Get(ctx context.Context, req *Request) error {
 		return err
 	}
 	if err == nil {
-		err = g.update(ctx, req.Dst, sshKeyFile, ref, depth)
+		err = g.update(ctx, req.Dst, sshKeyFile, ref, req.URL(), depth)
 	} else {
 		err = g.clone(ctx, sshKeyFile, depth, req)
 	}
@@ -193,28 +193,63 @@ func (g *GitGetter) clone(ctx context.Context, sshKeyFile string, depth int, req
 	return getRunCommand(cmd)
 }
 
-func (g *GitGetter) update(ctx context.Context, dst, sshKeyFile, ref string, depth int) error {
-	// Determine if we're a branch. If we're NOT a branch, then we just
-	// switch to master prior to checking out
-	cmd := exec.CommandContext(ctx, "git", "show-ref", "-q", "--verify", "refs/heads/"+ref)
+func (g *GitGetter) update(ctx context.Context, dst, sshKeyFile, ref string, u *url.URL, depth int) error {
+	// Remove all variations of .git directories
+	err := removeCaseInsensitiveGitDirectory(dst)
+	if err != nil {
+		return err
+
+	}
+
+	// Initialize the git repository
+	cmd := exec.CommandContext(ctx, "git", "init")
+	cmd.Dir = dst
+	err = getRunCommand(cmd)
+	if err != nil {
+		return err
+	}
+
+	// Add the git remote
+	cmd = exec.CommandContext(ctx, "git", "remote", "add", "origin", "--", u.String())
+	cmd.Dir = dst
+	err = getRunCommand(cmd)
+	if err != nil {
+		return err
+	}
+
+	// Fetch the remote ref
+	cmd = exec.CommandContext(ctx, "git", "fetch", "--tags")
+	cmd.Dir = dst
+	err = getRunCommand(cmd)
+	if err != nil {
+		return err
+	}
+
+	// Fetch the remote ref
+	cmd = exec.CommandContext(ctx, "git", "fetch", "origin", "--", ref)
 	cmd.Dir = dst
+	err = getRunCommand(cmd)
+	if err != nil {
+		return err
+	}
 
-	if getRunCommand(cmd) != nil {
-		// Not a branch, switch to default branch. This will also catch
-		// non-existent branches, in which case we want to switch to default
-		// and then checkout the proper branch later.
-		ref = findDefaultBranch(ctx, dst)
+	// Reset the branch to the fetched ref
+	cmd = exec.CommandContext(ctx, "git", "reset", "--hard", "FETCH_HEAD")
+	cmd.Dir = dst
+	err = getRunCommand(cmd)
+	if err != nil {
+		return err
 	}
 
-	// We have to be on a branch to pull
+	// Checkout ref branch
 	if err := g.checkout(ctx, dst, ref); err != nil {
 		return err
 	}
 
 	if depth > 0 {
-		cmd = exec.CommandContext(ctx, "git", "pull", "--depth", strconv.Itoa(depth), "--ff-only")
+		cmd = exec.CommandContext(ctx, "git", "pull", "origin", "--depth", strconv.Itoa(depth), "--ff-only", "--", ref)
 	} else {
-		cmd = exec.CommandContext(ctx, "git", "pull", "--ff-only")
+		cmd = exec.CommandContext(ctx, "git", "pull", "origin", "--ff-only", "--", ref)
 	}
 
 	cmd.Dir = dst
@@ -326,6 +361,28 @@ func checkGitVersion(ctx context.Context, min string) error {
 	return nil
 }
 
+// removeCaseInsensitiveGitDirectory removes all .git directory variations
+func removeCaseInsensitiveGitDirectory(dst string) error {
+	files, err := os.ReadDir(dst)
+	if err != nil {
+		return fmt.Errorf("Failed to read the destination directory %s during git update", dst)
+
+	}
+	for _, f := range files {
+		if strings.EqualFold(f.Name(), ".git") && f.IsDir() {
+			err := os.RemoveAll(filepath.Join(dst, f.Name()))
+			if err != nil {
+				return fmt.Errorf("Failed to remove the .git directory in the destination directory %s during git update", dst)
+
+			}
+
+		}
+
+	}
+	return nil
+
+}
+
 func (g *GitGetter) Detect(req *Request) (bool, error) {
 	src := req.Src
 	if len(src) == 0 {

get_git_test.go

@@ -138,6 +138,7 @@ func TestGitGetter_remoteWithoutMaster(t *testing.T) {
 	}
 
 	// Get again should work
+	req.Dst = testing_helper.TempDir(t)
 	if err := g.Get(ctx, req); err != nil {
 		t.Fatalf("err: %s", err)
 	}
@@ -841,6 +842,154 @@ func TestGitGetter_subdirectory_traversal(t *testing.T) {
 	}
 }
 
+func TestGitGetter_BadGitConfig(t *testing.T) {
+	if !testHasGit {
+		t.Log("git not found, skipping")
+		t.Skip()
+
+	}
+
+	ctx := context.Background()
+	g := new(GitGetter)
+	dst := testing_helper.TempDir(t)
+
+	url, err := url.Parse("https://github.com/hashicorp/go-getter")
+	if err != nil {
+		t.Fatal(err)
+
+	}
+
+	_, err = os.Stat(dst)
+	if err != nil && !os.IsNotExist(err) {
+		t.Fatalf(err.Error())
+	}
+
+	if err == nil {
+		// Update the repository containing the bad git config.
+		// This should remove the bad git config file and initialize a new one.
+		err = g.update(ctx, dst, testGitToken, "main", url, 1)
+
+	} else {
+		// Clone a repository with a git config file
+		req := &Request{
+			Dst: dst,
+			u:   url,
+		}
+		err = g.clone(ctx, testGitToken, 1, req)
+		if err != nil {
+			t.Fatalf(err.Error())
+
+		}
+
+		// Edit the git config file to simulate a bad git config
+		gitConfigPath := filepath.Join(dst, ".git", "config")
+		err = os.WriteFile(gitConfigPath, []byte("bad config"), 0600)
+		if err != nil {
+			t.Fatalf(err.Error())
+
+		}
+
+		// Update the repository containing the bad git config.
+		// This should remove the bad git config file and initialize a new one.
+		err = g.update(ctx, dst, testGitToken, "main", url, 1)
+
+	}
+	if err != nil {
+		t.Fatalf(err.Error())
+
+	}
+
+	// Check if the .git/config file contains "bad config"
+	gitConfigPath := filepath.Join(dst, ".git", "config")
+	configBytes, err := os.ReadFile(gitConfigPath)
+	if err != nil {
+		t.Fatalf(err.Error())
+
+	}
+	if strings.Contains(string(configBytes), "bad config") {
+		t.Fatalf("The .git/config file contains 'bad config'")
+
+	}
+
+}
+
+func TestGitGetter_BadGitDirName(t *testing.T) {
+	if !testHasGit {
+		t.Log("git not found, skipping")
+		t.Skip()
+
+	}
+
+	ctx := context.Background()
+	g := new(GitGetter)
+	dst := testing_helper.TempDir(t)
+
+	url, err := url.Parse("https://github.com/hashicorp/go-getter")
+	if err != nil {
+		t.Fatal(err)
+
+	}
+
+	_, err = os.Stat(dst)
+	if err != nil && !os.IsNotExist(err) {
+		t.Fatalf(err.Error())
+	}
+	if err == nil {
+		// Remove all variations of .git directories
+		err = removeCaseInsensitiveGitDirectory(dst)
+		if err != nil {
+			t.Fatalf(err.Error())
+
+		}
+
+	} else {
+		// Clone a repository with a git directory
+		req := &Request{
+			Dst: dst,
+			u:   url,
+		}
+		err = g.clone(ctx, testGitToken, 1, req)
+		if err != nil {
+			t.Fatalf(err.Error())
+
+		}
+
+		// Rename the .git directory to .GIT
+		oldPath := filepath.Join(dst, ".git")
+		newPath := filepath.Join(dst, ".GIT")
+		err = os.Rename(oldPath, newPath)
+		if err != nil {
+			t.Fatalf(err.Error())
+
+		}
+
+		// Remove all variations of .git directories
+		err = removeCaseInsensitiveGitDirectory(dst)
+		if err != nil {
+			t.Fatalf(err.Error())
+
+		}
+
+	}
+	if err != nil {
+		t.Fatalf(err.Error())
+
+	}
+
+	// Check if the .GIT directory exists
+	if _, err := os.Stat(filepath.Join(dst, ".GIT")); !os.IsNotExist(err) {
+		t.Fatalf(".GIT directory still exists")
+
+	}
+
+	// Check if the .git directory exists
+	if _, err := os.Stat(filepath.Join(dst, ".git")); !os.IsNotExist(err) {
+		t.Fatalf(".git directory still exists")
+
+	}
+
+}
+
 // gitRepo is a helper struct which controls a single temp git repo.
 type gitRepo struct {
 	t   *testing.T