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archive/tar: properly handle header-only "files" in Reader

Certain special type-flags, specifically 1, 2, 3, 4, 5, 6,
do not have a data section. Thus, regardless of what the size field
says, we should not attempt to read any data for these special types.

The relevant PAX and USTAR specification says:
<<<
If the typeflag field is set to specify a file to be of type 1 (a link)
or 2 (a symbolic link), the size field shall be specified as zero.
If the typeflag field is set to specify a file of type 5 (directory),
the size field shall be interpreted as described under the definition
of that record type. No data logical records are stored for types 1, 2, or 5.
If the typeflag field is set to 3 (character special file),
4 (block special file), or 6 (FIFO), the meaning of the size field is
unspecified by this volume of POSIX.1-2008, and no data logical records shall
be stored on the medium.
Additionally, for type 6, the size field shall be ignored when reading.
If the typeflag field is set to any other value, the number of logical
records written following the header shall be (size+511)/512, ignoring
any fraction in the result of the division.
>>>

Contrary to the specification, we do not assert that the size field
is zero for type 1 and 2 since we liberally accept non-conforming formats.

Change-Id: I666b601597cb9d7a50caa081813d90ca9cfc52ed
Reviewed-on: https://go-review.googlesource.com/16614
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Joe Tsai 2015-11-03 18:12:31 -08:00 committed by Vincent Batts
parent 2424f4e367
commit 7500c932c7
2 changed files with 122 additions and 95 deletions

View file

@ -769,97 +769,77 @@ func (tr *Reader) readOldGNUSparseMap(header []byte) []sparseEntry {
return sp
}
// readGNUSparseMap1x0 reads the sparse map as stored in GNU's PAX sparse format version 1.0.
// The sparse map is stored just before the file data and padded out to the nearest block boundary.
// readGNUSparseMap1x0 reads the sparse map as stored in GNU's PAX sparse format
// version 1.0. The format of the sparse map consists of a series of
// newline-terminated numeric fields. The first field is the number of entries
// and is always present. Following this are the entries, consisting of two
// fields (offset, numBytes). This function must stop reading at the end
// boundary of the block containing the last newline.
//
// Note that the GNU manual says that numeric values should be encoded in octal
// format. However, the GNU tar utility itself outputs these values in decimal.
// As such, this library treats values as being encoded in decimal.
func readGNUSparseMap1x0(r io.Reader) ([]sparseEntry, error) {
buf := make([]byte, 2*blockSize)
sparseHeader := buf[:blockSize]
var cntNewline int64
var buf bytes.Buffer
var blk = make([]byte, blockSize)
// readDecimal is a helper function to read a decimal integer from the sparse map
// while making sure to read from the file in blocks of size blockSize
readDecimal := func() (int64, error) {
// Look for newline
nl := bytes.IndexByte(sparseHeader, '\n')
if nl == -1 {
if len(sparseHeader) >= blockSize {
// This is an error
return 0, ErrHeader
// feedTokens copies data in numBlock chunks from r into buf until there are
// at least cnt newlines in buf. It will not read more blocks than needed.
var feedTokens = func(cnt int64) error {
for cntNewline < cnt {
if _, err := io.ReadFull(r, blk); err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return err
}
oldLen := len(sparseHeader)
newLen := oldLen + blockSize
if cap(sparseHeader) < newLen {
// There's more header, but we need to make room for the next block
copy(buf, sparseHeader)
sparseHeader = buf[:newLen]
} else {
// There's more header, and we can just reslice
sparseHeader = sparseHeader[:newLen]
}
// Now that sparseHeader is large enough, read next block
if _, err := io.ReadFull(r, sparseHeader[oldLen:newLen]); err != nil {
return 0, err
}
// leaving this function for io.Reader makes it more testable
if tr, ok := r.(*Reader); ok && tr.RawAccounting {
if _, err := tr.rawBytes.Write(sparseHeader[oldLen:newLen]); err != nil {
return 0, err
buf.Write(blk)
for _, c := range blk {
if c == '\n' {
cntNewline++
}
}
// Look for a newline in the new data
nl = bytes.IndexByte(sparseHeader[oldLen:newLen], '\n')
if nl == -1 {
// This is an error
return 0, ErrHeader
}
nl += oldLen // We want the position from the beginning
}
// Now that we've found a newline, read a number
n, err := strconv.ParseInt(string(sparseHeader[:nl]), 10, 0)
if err != nil {
return 0, ErrHeader
}
// Update sparseHeader to consume this number
sparseHeader = sparseHeader[nl+1:]
return n, nil
return nil
}
// Read the first block
if _, err := io.ReadFull(r, sparseHeader); err != nil {
// nextToken gets the next token delimited by a newline. This assumes that
// at least one newline exists in the buffer.
var nextToken = func() string {
cntNewline--
tok, _ := buf.ReadString('\n')
return tok[:len(tok)-1] // Cut off newline
}
// Parse for the number of entries.
// Use integer overflow resistant math to check this.
if err := feedTokens(1); err != nil {
return nil, err
}
// leaving this function for io.Reader makes it more testable
if tr, ok := r.(*Reader); ok && tr.RawAccounting {
if _, err := tr.rawBytes.Write(sparseHeader); err != nil {
return nil, err
}
numEntries, err := strconv.ParseInt(nextToken(), 10, 0) // Intentionally parse as native int
if err != nil || numEntries < 0 || int(2*numEntries) < int(numEntries) {
return nil, ErrHeader
}
// The first line contains the number of entries
numEntries, err := readDecimal()
if err != nil {
// Parse for all member entries.
// numEntries is trusted after this since a potential attacker must have
// committed resources proportional to what this library used.
if err := feedTokens(2 * numEntries); err != nil {
return nil, err
}
// Read all the entries
sp := make([]sparseEntry, 0, numEntries)
for i := int64(0); i < numEntries; i++ {
// Read the offset
offset, err := readDecimal()
offset, err := strconv.ParseInt(nextToken(), 10, 64)
if err != nil {
return nil, err
return nil, ErrHeader
}
// Read numBytes
numBytes, err := readDecimal()
numBytes, err := strconv.ParseInt(nextToken(), 10, 64)
if err != nil {
return nil, err
return nil, ErrHeader
}
sp = append(sp, sparseEntry{offset: offset, numBytes: numBytes})
}
return sp, nil
}

View file

@ -719,35 +719,82 @@ func TestReadGNUSparseMap0x1(t *testing.T) {
}
func TestReadGNUSparseMap1x0(t *testing.T) {
// This test uses lots of holes so the sparse header takes up more than two blocks
numEntries := 100
expected := make([]sparseEntry, 0, numEntries)
sparseMap := new(bytes.Buffer)
fmt.Fprintf(sparseMap, "%d\n", numEntries)
for i := 0; i < numEntries; i++ {
offset := int64(2048 * i)
numBytes := int64(1024)
expected = append(expected, sparseEntry{offset: offset, numBytes: numBytes})
fmt.Fprintf(sparseMap, "%d\n%d\n", offset, numBytes)
var sp = []sparseEntry{{1, 2}, {3, 4}}
for i := 0; i < 98; i++ {
sp = append(sp, sparseEntry{54321, 12345})
}
// Make the header the smallest multiple of blockSize that fits the sparseMap
headerBlocks := (sparseMap.Len() + blockSize - 1) / blockSize
bufLen := blockSize * headerBlocks
buf := make([]byte, bufLen)
copy(buf, sparseMap.Bytes())
var vectors = []struct {
input string // Input data
sparseMap []sparseEntry // Expected sparse entries to be outputted
cnt int // Expected number of bytes read
err error // Expected errors that may be raised
}{{
input: "",
cnt: 0,
err: io.ErrUnexpectedEOF,
}, {
input: "ab",
cnt: 2,
err: io.ErrUnexpectedEOF,
}, {
input: strings.Repeat("\x00", 512),
cnt: 512,
err: io.ErrUnexpectedEOF,
}, {
input: strings.Repeat("\x00", 511) + "\n",
cnt: 512,
err: ErrHeader,
}, {
input: strings.Repeat("\n", 512),
cnt: 512,
err: ErrHeader,
}, {
input: "0\n" + strings.Repeat("\x00", 510) + strings.Repeat("a", 512),
sparseMap: []sparseEntry{},
cnt: 512,
}, {
input: strings.Repeat("0", 512) + "0\n" + strings.Repeat("\x00", 510),
sparseMap: []sparseEntry{},
cnt: 1024,
}, {
input: strings.Repeat("0", 1024) + "1\n2\n3\n" + strings.Repeat("\x00", 506),
sparseMap: []sparseEntry{{2, 3}},
cnt: 1536,
}, {
input: strings.Repeat("0", 1024) + "1\n2\n\n" + strings.Repeat("\x00", 509),
cnt: 1536,
err: ErrHeader,
}, {
input: strings.Repeat("0", 1024) + "1\n2\n" + strings.Repeat("\x00", 508),
cnt: 1536,
err: io.ErrUnexpectedEOF,
}, {
input: "-1\n2\n\n" + strings.Repeat("\x00", 506),
cnt: 512,
err: ErrHeader,
}, {
input: "1\nk\n2\n" + strings.Repeat("\x00", 506),
cnt: 512,
err: ErrHeader,
}, {
input: "100\n1\n2\n3\n4\n" + strings.Repeat("54321\n0000000000000012345\n", 98) + strings.Repeat("\x00", 512),
cnt: 2560,
sparseMap: sp,
}}
// Get an reader to read the sparse map
r := bytes.NewReader(buf)
// Read the sparse map
sp, err := readGNUSparseMap1x0(r)
if err != nil {
t.Errorf("Unexpected error: %v", err)
}
if !reflect.DeepEqual(sp, expected) {
t.Errorf("Incorrect sparse map: got %v, wanted %v", sp, expected)
for i, v := range vectors {
r := strings.NewReader(v.input)
sp, err := readGNUSparseMap1x0(r)
if !reflect.DeepEqual(sp, v.sparseMap) && !(len(sp) == 0 && len(v.sparseMap) == 0) {
t.Errorf("test %d, readGNUSparseMap1x0(...): got %v, want %v", i, sp, v.sparseMap)
}
if numBytes := len(v.input) - r.Len(); numBytes != v.cnt {
t.Errorf("test %d, bytes read: got %v, want %v", i, numBytes, v.cnt)
}
if err != v.err {
t.Errorf("test %d, unexpected error: got %v, want %v", i, err, v.err)
}
}
}