archive/tar: forbid NUL character in string fields

USTAR and GNU strings are NUL-terminated. Thus, we should never
allow the NUL terminator, otherwise we will lose data round-trip.

Relevant specification text:
<<<
The fields magic, uname, and gname are character strings each terminated by a NUL character.
>>>

Technically, PAX keys and values should be UTF-8, but the observance
of invalid files in the wild causes us to be more liberal.
<<<
The <length> field, <blank>, <equals-sign>, and <newline> shown shall
be limited to the portable character set, as encoded in UTF-8.
>>>

Thus, we only reject NULs in PAX keys, and NULs for PAX values
representing the USTAR string fields (i.e., path, linkpath, uname, gname).
These are treated more strictly because they represent strings that
are typically represented as C-strings on POSIX systems.

Change-Id: I305b794d9d966faad852ff660bd0b3b0964e52bf
Reviewed-on: https://go-review.googlesource.com/14724
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/archive/tar/reader_test.go

@@ -335,6 +335,34 @@ func TestReader(t *testing.T) {
 			ModTime:  time.Unix(0, 0),
 			Typeflag: '2',
 		}},
+	}, {
+		// Both BSD and GNU tar truncate long names at first NUL even
+		// if there is data following that NUL character.
+		// This is reasonable as GNU long names are C-strings.
+		file: "testdata/gnu-long-nul.tar",
+		headers: []*Header{{
+			Name:     "0123456789",
+			Mode:     0644,
+			Uid:      1000,
+			Gid:      1000,
+			ModTime:  time.Unix(1486082191, 0),
+			Typeflag: '0',
+			Uname:    "rawr",
+			Gname:    "dsnet",
+		}},
+	}, {
+		// BSD tar v3.1.2 and GNU tar v1.27.1 both rejects PAX records
+		// with NULs in the key.
+		file: "testdata/pax-nul-xattrs.tar",
+		err:  ErrHeader,
+	}, {
+		// BSD tar v3.1.2 rejects a PAX path with NUL in the value, while
+		// GNU tar v1.27.1 simply truncates at first NUL.
+		// We emulate the behavior of BSD since it is strange doing NUL
+		// truncations since PAX records are length-prefix strings instead
+		// of NUL-terminated C-strings.
+		file: "testdata/pax-nul-path.tar",
+		err:  ErrHeader,
 	}, {
 		file: "testdata/neg-size.tar",
 		err:  ErrHeader,
@@ -358,11 +386,11 @@ func TestReader(t *testing.T) {
 		}},
 	}}
 
-	for i, v := range vectors {
+	for _, v := range vectors {
+		t.Run(path.Base(v.file), func(t *testing.T) {
 			f, err := os.Open(v.file)
 			if err != nil {
-			t.Errorf("file %s, test %d: unexpected error: %v", v.file, i, err)
-			continue
+				t.Fatalf("unexpected error: %v", err)
 			}
 			defer f.Close()
 
@@ -395,39 +423,34 @@ func TestReader(t *testing.T) {
 				chksums = append(chksums, fmt.Sprintf("%x", h.Sum(nil)))
 			}
 
-		for j, hdr := range hdrs {
-			if j >= len(v.headers) {
-				t.Errorf("file %s, test %d, entry %d: unexpected header:\ngot %+v",
-					v.file, i, j, *hdr)
+			for i, hdr := range hdrs {
+				if i >= len(v.headers) {
+					t.Fatalf("entry %d: unexpected header:\ngot %+v", i, *hdr)
 					continue
 				}
-			if !reflect.DeepEqual(*hdr, *v.headers[j]) {
-				t.Errorf("file %s, test %d, entry %d: incorrect header:\ngot  %+v\nwant %+v",
-					v.file, i, j, *hdr, *v.headers[j])
+				if !reflect.DeepEqual(*hdr, *v.headers[i]) {
+					t.Fatalf("entry %d: incorrect header:\ngot  %+v\nwant %+v", i, *hdr, *v.headers[i])
 				}
 			}
 			if len(hdrs) != len(v.headers) {
-			t.Errorf("file %s, test %d: got %d headers, want %d headers",
-				v.file, i, len(hdrs), len(v.headers))
+				t.Fatalf("got %d headers, want %d headers", len(hdrs), len(v.headers))
 			}
 
-		for j, sum := range chksums {
-			if j >= len(v.chksums) {
-				t.Errorf("file %s, test %d, entry %d: unexpected sum: got %s",
-					v.file, i, j, sum)
+			for i, sum := range chksums {
+				if i >= len(v.chksums) {
+					t.Fatalf("entry %d: unexpected sum: got %s", i, sum)
 					continue
 				}
-			if sum != v.chksums[j] {
-				t.Errorf("file %s, test %d, entry %d: incorrect checksum: got %s, want %s",
-					v.file, i, j, sum, v.chksums[j])
+				if sum != v.chksums[i] {
+					t.Fatalf("entry %d: incorrect checksum: got %s, want %s", i, sum, v.chksums[i])
 				}
 			}
 
 			if err != v.err {
-			t.Errorf("file %s, test %d: unexpected error: got %v, want %v",
-				v.file, i, err, v.err)
+				t.Fatalf("unexpected error: got %v, want %v", err, v.err)
 			}
 			f.Close()
+		})
 	}
 }
 

src/archive/tar/strconv.go

@@ -12,22 +12,25 @@ import (
 	"time"
 )
 
+// isASCII reports whether the input is an ASCII C-style string.
 func isASCII(s string) bool {
 	for _, c := range s {
-		if c >= 0x80 {
+		if c >= 0x80 || c == 0x00 {
 			return false
 		}
 	}
 	return true
 }
 
+// toASCII converts the input to an ASCII C-style string.
+// This a best effort conversion, so invalid characters are dropped.
 func toASCII(s string) string {
 	if isASCII(s) {
 		return s
 	}
 	var buf bytes.Buffer
 	for _, c := range s {
-		if c < 0x80 {
+		if c < 0x80 && c != 0x00 {
 			buf.WriteByte(byte(c))
 		}
 	}
@@ -232,12 +235,21 @@ func parsePAXRecord(s string) (k, v, r string, err error) {
 	if eq == -1 {
 		return "", "", s, ErrHeader
 	}
-	return rec[:eq], rec[eq+1:], rem, nil
+	k, v = rec[:eq], rec[eq+1:]
+
+	if !validPAXRecord(k, v) {
+		return "", "", s, ErrHeader
+	}
+	return k, v, rem, nil
 }
 
 // formatPAXRecord formats a single PAX record, prefixing it with the
 // appropriate length.
-func formatPAXRecord(k, v string) string {
+func formatPAXRecord(k, v string) (string, error) {
+	if !validPAXRecord(k, v) {
+		return "", ErrHeader
+	}
+
 	const padding = 3 // Extra padding for ' ', '=', and '\n'
 	size := len(k) + len(v) + padding
 	size += len(strconv.Itoa(size))
@@ -248,5 +260,19 @@ func formatPAXRecord(k, v string) string {
 		size = len(record)
 		record = fmt.Sprintf("%d %s=%s\n", size, k, v)
 	}
-	return record
+	return record, nil
+}
+
+// validPAXRecord reports whether the key-value pair is valid.
+// Keys and values should be UTF-8, but the number of bad writers out there
+// forces us to be a more liberal.
+// Thus, we only reject all keys with NUL, and only reject NULs in values
+// for the PAX version of the USTAR string fields.
+func validPAXRecord(k, v string) bool {
+	switch k {
+	case paxPath, paxLinkpath, paxUname, paxGname:
+		return strings.IndexByte(v, 0) < 0
+	default:
+		return strings.IndexByte(k, 0) < 0
+	}
 }

src/archive/tar/strconv_test.go

@@ -256,7 +256,7 @@ func TestParsePAXRecord(t *testing.T) {
 		{"18 foo=b=\nar=\n==\x00\n", "", "foo", "b=\nar=\n==\x00", true},
 		{"27 foo=hello9 foo=ba\nworld\n", "", "foo", "hello9 foo=ba\nworld", true},
 		{"27 ☺☻☹=日a本b語ç\nmeow mix", "meow mix", "☺☻☹", "日a本b語ç", true},
-		{"17 \x00hello=\x00world\n", "", "\x00hello", "\x00world", true},
+		{"17 \x00hello=\x00world\n", "17 \x00hello=\x00world\n", "", "", false},
 		{"1 k=1\n", "1 k=1\n", "", "", false},
 		{"6 k~1\n", "6 k~1\n", "", "", false},
 		{"6_k=1\n", "6_k=1\n", "", "", false},
@@ -296,21 +296,33 @@ func TestFormatPAXRecord(t *testing.T) {
 		inKey string
 		inVal string
 		want  string
+		ok    bool
 	}{
-		{"k", "v", "6 k=v\n"},
-		{"path", "/etc/hosts", "19 path=/etc/hosts\n"},
-		{"path", longName, "210 path=" + longName + "\n"},
-		{"path", medName, "110 path=" + medName + "\n"},
-		{"foo", "ba", "9 foo=ba\n"},
-		{"foo", "bar", "11 foo=bar\n"},
-		{"foo", "b=\nar=\n==\x00", "18 foo=b=\nar=\n==\x00\n"},
-		{"foo", "hello9 foo=ba\nworld", "27 foo=hello9 foo=ba\nworld\n"},
-		{"☺☻☹", "日a本b語ç", "27 ☺☻☹=日a本b語ç\n"},
-		{"\x00hello", "\x00world", "17 \x00hello=\x00world\n"},
+		{"k", "v", "6 k=v\n", true},
+		{"path", "/etc/hosts", "19 path=/etc/hosts\n", true},
+		{"path", longName, "210 path=" + longName + "\n", true},
+		{"path", medName, "110 path=" + medName + "\n", true},
+		{"foo", "ba", "9 foo=ba\n", true},
+		{"foo", "bar", "11 foo=bar\n", true},
+		{"foo", "b=\nar=\n==\x00", "18 foo=b=\nar=\n==\x00\n", true},
+		{"foo", "hello9 foo=ba\nworld", "27 foo=hello9 foo=ba\nworld\n", true},
+		{"☺☻☹", "日a本b語ç", "27 ☺☻☹=日a本b語ç\n", true},
+		{"xhello", "\x00world", "17 xhello=\x00world\n", true},
+		{"path", "null\x00", "", false},
+		{"null\x00", "value", "", false},
+		{paxXattr + "key", "null\x00", "26 SCHILY.xattr.key=null\x00\n", true},
 	}
 
 	for _, v := range vectors {
-		got := formatPAXRecord(v.inKey, v.inVal)
+		got, err := formatPAXRecord(v.inKey, v.inVal)
+		ok := (err == nil)
+		if ok != v.ok {
+			if v.ok {
+				t.Errorf("formatPAXRecord(%q, %q): got format failure, want success", v.inKey, v.inVal)
+			} else {
+				t.Errorf("formatPAXRecord(%q, %q): got format success, want failure", v.inKey, v.inVal)
+			}
+		}
 		if got != v.want {
 			t.Errorf("formatPAXRecord(%q, %q): got %q, want %q",
 				v.inKey, v.inVal, got, v.want)

src/archive/tar/writer.go

@@ -308,7 +308,11 @@ func (tw *Writer) writePAXHeader(hdr *Header, paxHeaders map[string]string) erro
 	sort.Strings(keys)
 
 	for _, k := range keys {
-		fmt.Fprint(&buf, formatPAXRecord(k, paxHeaders[k]))
+		rec, err := formatPAXRecord(k, paxHeaders[k])
+		if err != nil {
+			return err
+		}
+		fmt.Fprint(&buf, rec)
 	}
 
 	ext.Size = int64(len(buf.Bytes()))

src/archive/tar/writer_test.go

@@ -10,6 +10,7 @@ import (
 	"io"
 	"io/ioutil"
 	"os"
+	"path"
 	"reflect"
 	"sort"
 	"strings"
@@ -51,6 +52,7 @@ func TestWriter(t *testing.T) {
 	vectors := []struct {
 		file    string // filename of expected output
 		entries []*entry
+		err     error // expected error on WriteHeader
 	}{{
 		// The writer test file was produced with this command:
 		// tar (GNU tar) 1.26
@@ -200,45 +202,58 @@ func TestWriter(t *testing.T) {
 			},
 			// no contents
 		}},
+	}, {
+		entries: []*entry{{
+			header: &Header{
+				Name:     "bad-null.txt",
+				Typeflag: '0',
+				Xattrs:   map[string]string{"null\x00null\x00": "fizzbuzz"},
+			},
+		}},
+		err: ErrHeader,
+	}, {
+		entries: []*entry{{
+			header: &Header{
+				Name:     "null\x00.txt",
+				Typeflag: '0',
+			},
+		}},
+		err: ErrHeader,
 	}}
 
-testLoop:
-	for i, v := range vectors {
-		expected, err := ioutil.ReadFile(v.file)
-		if err != nil {
-			t.Errorf("test %d: Unexpected error: %v", i, err)
-			continue
-		}
-
+	for _, v := range vectors {
+		t.Run(path.Base(v.file), func(t *testing.T) {
 			buf := new(bytes.Buffer)
 			tw := NewWriter(iotest.TruncateWriter(buf, 4<<10)) // only catch the first 4 KB
-		big := false
-		for j, entry := range v.entries {
-			big = big || entry.header.Size > 1<<10
-			if err := tw.WriteHeader(entry.header); err != nil {
-				t.Errorf("test %d, entry %d: Failed writing header: %v", i, j, err)
-				continue testLoop
+			canFail := false
+			for i, entry := range v.entries {
+				canFail = canFail || entry.header.Size > 1<<10 || v.err != nil
+
+				err := tw.WriteHeader(entry.header)
+				if err != v.err {
+					t.Fatalf("entry %d: WriteHeader() = %v, want %v", i, err, v.err)
 				}
 				if _, err := io.WriteString(tw, entry.contents); err != nil {
-				t.Errorf("test %d, entry %d: Failed writing contents: %v", i, j, err)
-				continue testLoop
+					t.Fatalf("entry %d: WriteString() = %v, want nil", i, err)
 				}
 			}
 			// Only interested in Close failures for the small tests.
-		if err := tw.Close(); err != nil && !big {
-			t.Errorf("test %d: Failed closing archive: %v", i, err)
-			continue testLoop
+			if err := tw.Close(); err != nil && !canFail {
+				t.Fatalf("Close() = %v, want nil", err)
 			}
 
-		actual := buf.Bytes()
-		if !bytes.Equal(expected, actual) {
-			t.Errorf("test %d: Incorrect result: (-=expected, +=actual)\n%v",
-				i, bytediff(expected, actual))
+			if v.file != "" {
+				want, err := ioutil.ReadFile(v.file)
+				if err != nil {
+					t.Fatalf("ReadFile() = %v, want nil", err)
 				}
-		if testing.Short() { // The second test is expensive.
-			break
+				got := buf.Bytes()
+				if !bytes.Equal(want, got) {
+					t.Fatalf("incorrect result: (-=want, +=got)\n%v", bytediff(want, got))
 				}
 			}
+		})
+	}
 }
 
 func TestPax(t *testing.T) {