fix: git artifactory arbitrary file read issue (#1965)

Signed-off-by: Derek Wang <whynowy@gmail.com>

sensors/artifacts/git.go

@@ -20,6 +20,8 @@ import (
 	"fmt"
 	"io/ioutil"
 	"os"
+	"path"
+	"strings"
 
 	"github.com/go-git/go-git/v5"
 	"github.com/go-git/go-git/v5/config"
@@ -44,6 +46,8 @@ var (
 		"refs/*:refs/*",
 		"HEAD:refs/heads/HEAD",
 	}
+
+	notAllowedInPath = []string{"..", "~", "\\"}
 )
 
 type GitArtifactReader struct {
@@ -52,6 +56,15 @@ type GitArtifactReader struct {
 
 // NewGitReader returns a new git reader
 func NewGitReader(gitArtifact *v1alpha1.GitArtifact) (*GitArtifactReader, error) {
+	if gitArtifact == nil {
+		return nil, fmt.Errorf("nil git artifact")
+	}
+	for _, na := range notAllowedInPath {
+		if strings.Contains(gitArtifact.FilePath, na) {
+			return nil, fmt.Errorf("%q is not allowed in the filepath", na)
+		}
+	}
+
 	return &GitArtifactReader{
 		artifact: gitArtifact,
 	}, nil
@@ -176,8 +189,16 @@ func (g *GitArtifactReader) readFromRepository(r *git.Repository, dir string) ([
 			return nil, fmt.Errorf("failed to pull latest updates. err: %+v", err)
 		}
 	}
-
-	return ioutil.ReadFile(fmt.Sprintf("%s/%s", dir, g.artifact.FilePath))
+	filePath := fmt.Sprintf("%s/%s", dir, g.artifact.FilePath)
+	// symbol link is not allowed due to security concern
+	isSymbolLink, err := isSymbolLink(filePath)
+	if err != nil {
+		return nil, err
+	}
+	if isSymbolLink {
+		return nil, fmt.Errorf("%q is a symbol link which is not allowed", g.artifact.FilePath)
+	}
+	return ioutil.ReadFile(filePath)
 }
 
 func (g *GitArtifactReader) getBranchOrTag() *git.CheckoutOptions {
@@ -241,3 +262,14 @@ func (g *GitArtifactReader) Read() ([]byte, error) {
 	}
 	return g.readFromRepository(r, cloneDir)
 }
+
+func isSymbolLink(filepath string) (bool, error) {
+	fi, err := os.Lstat(path.Clean(filepath))
+	if err != nil {
+		return false, err
+	}
+	if fi.Mode()&os.ModeSymlink != 0 {
+		return true, nil
+	}
+	return false, nil
+}