dont let the dictionary be larger than the unpacked file size

Author: nwaples

archive.go

@@ -89,7 +89,7 @@ type fileBlockHeader struct {
 	packedOff int64            // offset to data in packed file
 	blocknum  int              // number for current block in file
 	volnum    int              // archive volume number
-	winSize   int              // decode window size
+	winSize   int64            // decode window size
 	hash      func() hash.Hash // hash used for file checksum
 	hashKey   []byte           // optional hmac key to be used calculate file checksum
 	sum       []byte           // expected checksum for file contents

archive50.go

@@ -8,7 +8,6 @@ import (
 	"hash"
 	"hash/crc32"
 	"io"
-	"math"
 	"math/bits"
 	"slices"
 	"time"
@@ -374,28 +373,21 @@ func (a *archive50) parseFileHeader(h *blockHeader50) (*fileBlockHeader, error)
 	method := (flags >> 7) & 7 // compression method (0 == none)
 	if f.first && method != 0 {
 		unpackver := flags & file5CompAlgorithm
-		var winSize int64
-		if unpackver == 0 {
+		switch unpackver {
+		case 0:
 			f.decVer = decode50Ver
-			winSize = 0x20000 << ((flags >> 10) & 0x0F)
-		} else if unpackver == 1 {
+			f.winSize = 0x20000 << ((flags >> 10) & 0x0F)
+		case 1:
 			if flags&file5CompV5Compat > 0 {
 				f.decVer = decode50Ver
 			} else {
 				f.decVer = decode70Ver
 			}
-			winSize = 0x20000 << ((flags >> 10) & 0x1F)
-			winSize += winSize / 32 * int64((flags>>15)&0x1F)
-			if winSize > maxDictSize {
-				return nil, ErrDictionaryTooLarge
-			}
-		} else {
+			f.winSize = 0x20000 << ((flags >> 10) & 0x1F)
+			f.winSize += f.winSize / 32 * int64((flags>>15)&0x1F)
+		default:
 			return nil, ErrUnknownDecoder
 		}
-		if winSize > math.MaxInt {
-			return nil, ErrPlatformIntSize
-		}
-		f.winSize = int(winSize)
 	}
 	switch h.data.uvarint() {
 	case 0:

reader.go

@@ -8,6 +8,7 @@ import (
 	"hash"
 	"io"
 	"io/fs"
+	"math"
 	"sync"
 	"time"
 )
@@ -331,7 +332,17 @@ func (pr *packedFileReader) newArchiveFileFrom(r archiveFile, blocks *fileBlockL
 		if pr.dr == nil {
 			pr.dr = new(decodeReader)
 		}
-		err := pr.dr.init(r, h.decVer, h.winSize, !h.Solid, h.arcSolid, h.UnPackedSize)
+		// doesn't make sense for the dictionary to be larger than the file
+		if !h.UnKnownSize && h.winSize > h.UnPackedSize {
+			h.winSize = h.UnPackedSize
+		}
+		if h.winSize > maxDictSize {
+			return nil, ErrDictionaryTooLarge
+		}
+		if h.winSize > math.MaxInt {
+			return nil, ErrPlatformIntSize
+		}
+		err := pr.dr.init(r, h.decVer, int(h.winSize), !h.Solid, h.arcSolid, h.UnPackedSize)
 		if err != nil {
 			return nil, err
 		}