From 2c13842451223261c5e585f527f1732e510db60d Mon Sep 17 00:00:00 2001
From: Cole Wippern <cgwippern@google.com>
Date: Tue, 12 Nov 2019 17:07:12 -0800
Subject: [PATCH] Resolve symlink paths

---
 pkg/commands/copy.go | 26 ++++++++++++++++++++++++++
 pkg/util/fs_util.go  |  8 +++++++-
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/pkg/commands/copy.go b/pkg/commands/copy.go
index 15f778e8de..ad75f6f3f2 100644
--- a/pkg/commands/copy.go
+++ b/pkg/commands/copy.go
@@ -66,6 +66,14 @@ func (c *CopyCommand) ExecuteCommand(config *v1.Config, buildArgs *dockerfile.Bu
 		if err != nil {
 			return err
 		}
+
+		// If the destination dir is a symlink we need to resolve the path and use
+		// that instead of the symlink path
+		destPath, err = resolveIfSymlink(destPath)
+		if err != nil {
+			return err
+		}
+
 		if fi.IsDir() {
 			if !filepath.IsAbs(dest) {
 				// we need to add '/' to the end to indicate the destination is a directory
@@ -178,3 +186,21 @@ func (cr *CachingCopyCommand) FilesToSnapshot() []string {
 func (cr *CachingCopyCommand) String() string {
 	return cr.cmd.String()
 }
+
+func resolveIfSymlink(destPath string) (string, error) {
+	baseDir := filepath.Dir(destPath)
+	if info, err := os.Lstat(baseDir); err == nil {
+		switch mode := info.Mode(); {
+		case mode&os.ModeSymlink != 0:
+			linkPath, err := os.Readlink(baseDir)
+			if err != nil {
+				return "", errors.Wrap(err, "error reading symlink")
+			}
+			absLinkPath := filepath.Join(filepath.Dir(baseDir), linkPath)
+			newPath := filepath.Join(absLinkPath, filepath.Base(destPath))
+			logrus.Tracef("Updating destination path from %v to %v due to symlink", destPath, newPath)
+			return newPath, nil
+		}
+	}
+	return destPath, nil
+}
diff --git a/pkg/util/fs_util.go b/pkg/util/fs_util.go
index 00562e56f3..10fccb7f7b 100644
--- a/pkg/util/fs_util.go
+++ b/pkg/util/fs_util.go
@@ -424,11 +424,17 @@ func FilepathExists(path string) bool {
 func CreateFile(path string, reader io.Reader, perm os.FileMode, uid uint32, gid uint32) error {
 	// Create directory path if it doesn't exist
 	baseDir := filepath.Dir(path)
-	if _, err := os.Lstat(baseDir); os.IsNotExist(err) {
+	if info, err := os.Lstat(baseDir); os.IsNotExist(err) {
 		logrus.Tracef("baseDir %s for file %s does not exist. Creating.", baseDir, path)
 		if err := os.MkdirAll(baseDir, 0755); err != nil {
 			return err
 		}
+	} else {
+		switch mode := info.Mode(); {
+		case mode&os.ModeSymlink != 0:
+			logrus.Infof("destination cannot be a symlink %v", baseDir)
+			return errors.New("destination cannot be a symlink")
+		}
 	}
 	dest, err := os.Create(path)
 	if err != nil {