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crypt: Fix data corruption on seek
This was caused by failing to reset the internal buffer on seek so old data was read first before the new data. The unit tests didn't detect this because they were reading to the end of the file to check integrity and thus emptying the internal buffer. Both code and unit tests were fixed up.
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@ -604,9 +604,20 @@ func (fh *decrypter) Seek(offset int64, whence int) (int64, error) {
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return 0, fh.err
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}
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// Can we seek it directly?
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// blocks we need to seek, plus bytes we need to discard
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blocks, discard := offset/blockDataSize, offset%blockDataSize
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// Offset in underlying stream we need to seek
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underlyingOffset := int64(fileHeaderSize) + blocks*(blockHeaderSize+blockDataSize)
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// Move the nonce on the correct number of blocks from the start
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fh.nonce = fh.initialNonce
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fh.nonce.add(uint64(blocks))
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// Can we seek underlying stream directly?
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if do, ok := fh.rc.(io.Seeker); ok {
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_, err := do.Seek(offset, 0)
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// Seek underlying stream directly
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_, err := do.Seek(underlyingOffset, 0)
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if err != nil {
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return 0, fh.finish(err)
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}
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@ -615,16 +626,6 @@ func (fh *decrypter) Seek(offset int64, whence int) (int64, error) {
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_ = fh.rc.Close() // close underlying file
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fh.rc = nil
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// blocks we need to seek, plus bytes we need to discard
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blocks, discard := offset/blockDataSize, offset%blockDataSize
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// Offset in underlying stream we need to seek
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underlyingOffset := int64(fileHeaderSize) + blocks*(blockHeaderSize+blockDataSize)
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// Move the nonce on the correct number of blocks from the start
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fh.nonce = fh.initialNonce
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fh.nonce.add(uint64(blocks))
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// Re-open the underlying object with the offset given
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rc, err := fh.open(underlyingOffset)
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if err != nil {
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@ -633,12 +634,16 @@ func (fh *decrypter) Seek(offset int64, whence int) (int64, error) {
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// Set the file handle
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fh.rc = rc
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}
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// Discard excess bytes
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_, err = io.CopyN(ioutil.Discard, fh, discard)
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if err != nil {
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return 0, fh.finish(err)
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}
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// Empty the buffer
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fh.bufIndex = 0
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fh.bufSize = 0
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// Discard excess bytes
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_, err := io.CopyN(ioutil.Discard, fh, discard)
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if err != nil {
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return 0, fh.finish(err)
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}
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return offset, nil
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@ -881,15 +881,26 @@ func TestNewDecrypterSeek(t *testing.T) {
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return ioutil.NopCloser(bytes.NewBuffer(ciphertext[int(underlyingOffset):])), nil
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}
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inBlock := make([]byte, 1024)
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// Check the seek worked by reading a block and checking it
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// against what it should be
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check := func(rc ReadSeekCloser, offset int) {
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n, err := io.ReadFull(rc, inBlock)
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if err != nil && err != io.EOF && err != io.ErrUnexpectedEOF {
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require.NoError(t, err)
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}
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seekedDecrypted := inBlock[:n]
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require.Equal(t, plaintext[offset:offset+n], seekedDecrypted)
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}
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// Now try decoding it with a open/seek
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for _, offset := range trials {
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rc, err := c.DecryptDataSeek(open, int64(offset))
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assert.NoError(t, err)
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seekedDecrypted, err := ioutil.ReadAll(rc)
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assert.NoError(t, err)
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assert.Equal(t, plaintext[offset:], seekedDecrypted)
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check(rc, offset)
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}
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// Now try decoding it with a single open and lots of seeks
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@ -898,10 +909,7 @@ func TestNewDecrypterSeek(t *testing.T) {
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_, err := rc.Seek(int64(offset), 0)
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assert.NoError(t, err)
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seekedDecrypted, err := ioutil.ReadAll(rc)
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assert.NoError(t, err)
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assert.Equal(t, plaintext[offset:], seekedDecrypted)
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check(rc, offset)
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}
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}
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