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archive/tar: fix issues with readGNUSparseMap1x0
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Motivations:
* Use of strconv.ParseInt does not properly treat integers as 64bit,
preventing this function from working properly on 32bit machines.
* Use of io.ReadFull does not properly detect truncated streams
when the file suddenly ends on a block boundary.
* The function blindly trusts user input for numEntries and allocates
memory accordingly.
* The function does not validate that numEntries is not negative,
allowing a malicious sparse file to cause a panic during make.

In general, this function was overly complicated for what it was
accomplishing and it was hard to reason that it was free from
bounds errors. Instead, it has been rewritten and relies on
bytes.Buffer.ReadString to do the main work. So long as invariants
about the number of '\n' in the buffer are maintained, it is much
easier to see why this approach is correct.

Change-Id: Ibb12c4126c26e0ea460ea063cd17af68e3cf609e
Reviewed-on: https://go-review.googlesource.com/15174
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
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@dsnet @bradfitz
dsnet authored and bradfitz committed Dec 1, 2015
1 parent dd5e14a commit 7823197
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Showing 2 changed files with 124 additions and 85 deletions.
110 changes: 51 additions & 59 deletions src/archive/tar/reader.go
View file
Expand Up @@ -680,85 +680,77 @@ 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]

// 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
}
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
var cntNewline int64
var buf bytes.Buffer
var blk = make([]byte, blockSize)

// 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
}

// 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
buf.Write(blk)
for _, c := range blk {
if c == '\n' {
cntNewline++
}
}
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
}
return nil
}

// Update sparseHeader to consume this number
sparseHeader = sparseHeader[nl+1:]
return n, 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
}

// Read the first block
if _, err := io.ReadFull(r, sparseHeader); err != nil {
// Parse for the number of entries.
// Use integer overflow resistant math to check this.
if err := feedTokens(1); 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
}

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99 changes: 73 additions & 26 deletions src/archive/tar/reader_test.go
View file
Expand Up @@ -727,35 +727,82 @@ 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())

// Get an reader to read the sparse map
r := bytes.NewReader(buf)
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,
}}

// 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)
}
}
}

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