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fix(protocol): always expect & validate block hash in requests (#10738)

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Verify that block requests have a hash and that it's correct. This helps
prevent certain races and ensure that only expected data is ever
returned in response to a request.

(In Syncthing prior to 1.28.1 the block hash was omitted for encrypted
requests from trusted devices. This breaks compatibility with that
specific config on those versions.)

---------

Signed-off-by: Jakob Borg <jakob@kastelo.net>
This commit is contained in:
Jakob Borg
2026-06-11 18:51:25 +02:00
committed by GitHub
parent a5cbeeafea
commit f6428af4c8
6 changed files with 47 additions and 45 deletions
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lib/protocol/encryption.go
+13 -19
View File
@@ -93,31 +93,25 @@ func (e encryptedModel) Request(req *Request) (RequestResponse, error) {
}
realSize := req.Size - blockOverhead
realOffset := req.Offset - int64(req.BlockNo*blockOverhead)
if realOffset < 0 {
panic("bug: realOffset underflow")
}
if req.Size < minPaddedSize {
return nil, errors.New("short request")
}
// Attempt to decrypt the block hash; it may be nil depending on what
// type of device the request comes from. Trusted devices with
// encryption enabled know the hash but don't bother to encrypt & send
// it to us. Untrusted devices have the hash from the encrypted index
// data and do send it. The model knows to only verify the hash if it
// actually gets one.
var realHash []byte
// Decrypt the block hash.
fileKey := e.keyGen.FileKey(realName, folderKey)
if len(req.Hash) > 0 {
var additional [8]byte
binary.BigEndian.PutUint64(additional[:], uint64(realOffset))
realHash, err = decryptDeterministic(req.Hash, fileKey, additional[:])
if err != nil {
// "Legacy", no offset additional data?
realHash, err = decryptDeterministic(req.Hash, fileKey, nil)
}
if err != nil {
return nil, fmt.Errorf("decrypting block hash: %w", err)
}
var additional [8]byte
binary.BigEndian.PutUint64(additional[:], uint64(realOffset))
realHash, err := decryptDeterministic(req.Hash, fileKey, additional[:])
if err != nil {
// "Legacy", no offset additional data?
realHash, err = decryptDeterministic(req.Hash, fileKey, nil)
}
if err != nil {
return nil, fmt.Errorf("decrypting block hash: %w", err)
}
// Perform that request and grab the data.