keywords: safely encode symlink keywords

symlink(2) is a very dumb syscall, and allows you to put any damn value
you please inside a symlink. In addition, spaces are valid path
characters which causes issues with keyword parsing. So use Vis() and
Unvis() to safely store an encoded version of the path.

This also adds a cli test for this behaviour.

Signed-off-by: Aleksa Sarai <asarai@suse.de>

keywords.go

@@ -297,7 +297,11 @@ var (
 	linkKeywordFunc = func(path string, info os.FileInfo, r io.Reader) (string, error) {
 		if sys, ok := info.Sys().(*tar.Header); ok {
 			if sys.Linkname != "" {
-				return fmt.Sprintf("link=%s", sys.Linkname), nil
+				linkname, err := Vis(sys.Linkname)
+				if err != nil {
+					return "", err
+				}
+				return fmt.Sprintf("link=%s", linkname), nil
 			}
 			return "", nil
 		}
@@ -307,7 +311,11 @@ var (
 			if err != nil {
 				return "", err
 			}
-			return fmt.Sprintf("link=%s", str), nil
+			linkname, err := Vis(str)
+			if err != nil {
+				return "", err
+			}
+			return fmt.Sprintf("link=%s", linkname), nil
 		}
 		return "", nil
 	}

tar.go

@@ -129,7 +129,11 @@ func (ts *tarStream) readHeaders() {
 				log.Println(err)
 				break
 			}
-			linkname := KeyVal(kv).Value()
+			linkname, err := Unvis(KeyVal(kv).Value())
+			if err != nil {
+				log.Println(err)
+				break
+			}
 			if _, ok := ts.hardlinks[linkname]; !ok {
 				ts.hardlinks[linkname] = []string{hdr.Name}
 			} else {

test/cli/0002.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+set -e
+
+name=$(basename $0)
+root=$1
+gomtree=$(readlink -f ${root}/gomtree)
+t=$(mktemp -d /tmp/go-mtree.XXXXXX)
+
+echo "[${name}] Running in ${t}"
+# This test is for basic running check of manifest, and check against tar and file system
+#
+
+pushd ${root}
+
+# Create a symlink with spaces in the entries.
+mkdir ${t}/root
+ln -s "this is a dummy symlink" ${t}/root/link
+
+# Create manifest and check it against the same symlink.
+${gomtree} -K link,sha256digest -c -p ${t}/root > ${t}/root.mtree
+${gomtree} -K link,sha256digest -f ${t}/root.mtree -p ${t}/root
+
+popd
+rm -rf ${t}