PutObjectPart: set SSE-KMS headers and truncate ETags. (#14578)

This commit fixes two bugs in the `PutObjectPartHandler`.
First, `PutObjectPart` should return SSE-KMS headers
when the object is encrypted using SSE-KMS.
Before, this was not the case.

Second, the ETag should always be a 16 byte hex string,
perhaps followed by a `-X` (where `X` is the number of parts).
However, `PutObjectPart` used to return the encrypted ETag
in case of SSE-KMS. This leaks MinIO internal etag details
through the S3 API.

The combination of both bugs causes clients that use SSE-KMS
to fail when trying to validate the ETag. Since `PutObjectPart`
did not send the SSE-KMS response headers, the response looked
like a plaintext `PutObjectPart` response. Hence, the client
tries to verify that the ETag is the content-md5 of the part.
This could never be the case, since MinIO used to return the
encrypted ETag.

Therefore, clients behaving as specified by the S3 protocol
tried to verify the ETag in a situation they should not.

Signed-off-by: Andreas Auernhammer <hi@aead.dev>

cmd/encryption-v1.go

@@ -71,11 +71,19 @@ const (
 )
 
 // KMSKeyID returns in AWS compatible KMS KeyID() format.
-func (o ObjectInfo) KMSKeyID() string {
+func (o *ObjectInfo) KMSKeyID() string { return kmsKeyIDFromMetadata(o.UserDefined) }
-	if len(o.UserDefined) == 0 {
+
+// KMSKeyID returns in AWS compatible KMS KeyID() format.
+func (o *MultipartInfo) KMSKeyID() string { return kmsKeyIDFromMetadata(o.UserDefined) }
+
+// kmsKeyIDFromMetadata returns any AWS S3 KMS key ID in the
+// metadata, if any. It returns an empty ID if no key ID is
+// present.
+func kmsKeyIDFromMetadata(metadata map[string]string) string {
+	if len(metadata) == 0 {
 		return ""
 	}
-	kmsID, ok := o.UserDefined[crypto.MetaKeyID]
+	kmsID, ok := metadata[crypto.MetaKeyID]
 	if !ok {
 		return ""
 	}

cmd/object-handlers.go

@@ -2903,12 +2903,20 @@ func (api objectAPIHandlers) PutObjectPartHandler(w http.ResponseWriter, r *http
 	}
 
 	etag := partInfo.ETag
-	switch kind, encrypted := crypto.IsEncrypted(mi.UserDefined); {
+	if kind, encrypted := crypto.IsEncrypted(mi.UserDefined); encrypted {
-	case encrypted:
 		switch kind {
+		case crypto.S3KMS:
+			w.Header().Set(xhttp.AmzServerSideEncryption, xhttp.AmzEncryptionKMS)
+			w.Header().Set(xhttp.AmzServerSideEncryptionKmsID, mi.KMSKeyID())
+			if kmsCtx, ok := mi.UserDefined[crypto.MetaContext]; ok {
+				w.Header().Set(xhttp.AmzServerSideEncryptionKmsContext, kmsCtx)
+			}
+			if len(etag) >= 32 && strings.Count(etag, "-") != 1 {
+				etag = etag[len(etag)-32:]
+			}
 		case crypto.S3:
 			w.Header().Set(xhttp.AmzServerSideEncryption, xhttp.AmzEncryptionAES)
-			etag = tryDecryptETag(objectEncryptionKey[:], etag, false)
+			etag, _ = DecryptETag(objectEncryptionKey, ObjectInfo{ETag: etag})
 		case crypto.SSEC:
 			w.Header().Set(xhttp.AmzServerSideEncryptionCustomerAlgorithm, r.Header.Get(xhttp.AmzServerSideEncryptionCustomerAlgorithm))
 			w.Header().Set(xhttp.AmzServerSideEncryptionCustomerKeyMD5, r.Header.Get(xhttp.AmzServerSideEncryptionCustomerKeyMD5))
@@ -3175,66 +3183,6 @@ func (api objectAPIHandlers) CompleteMultipartUploadHandler(w http.ResponseWrite
 		return
 	}
 
-	var objectEncryptionKey []byte
-	var isEncrypted, ssec bool
-	if objectAPI.IsEncryptionSupported() {
-		mi, err := objectAPI.GetMultipartInfo(ctx, bucket, object, uploadID, ObjectOptions{})
-		if err != nil {
-			writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
-			return
-		}
-		if _, ok := crypto.IsEncrypted(mi.UserDefined); ok {
-			var key []byte
-			isEncrypted = true
-			ssec = crypto.SSEC.IsEncrypted(mi.UserDefined)
-			if crypto.S3.IsEncrypted(mi.UserDefined) {
-				// Calculating object encryption key
-				objectEncryptionKey, err = decryptObjectInfo(key, bucket, object, mi.UserDefined)
-				if err != nil {
-					writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
-					return
-				}
-			}
-		}
-	}
-
-	partsMap := make(map[string]PartInfo)
-	if isEncrypted {
-		maxParts := 10000
-		listPartsInfo, err := objectAPI.ListObjectParts(ctx, bucket, object, uploadID, 0, maxParts, ObjectOptions{})
-		if err != nil {
-			writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
-			return
-		}
-		for _, part := range listPartsInfo.Parts {
-			partsMap[strconv.Itoa(part.PartNumber)] = part
-		}
-	}
-
-	// Complete parts.
-	completeParts := make([]CompletePart, 0, len(complMultipartUpload.Parts))
-	originalCompleteParts := make([]CompletePart, 0, len(complMultipartUpload.Parts))
-	for _, part := range complMultipartUpload.Parts {
-		part.ETag = canonicalizeETag(part.ETag)
-		originalCompleteParts = append(originalCompleteParts, part)
-		if isEncrypted {
-			// ETag is stored in the backend in encrypted form. Validate client sent ETag with
-			// decrypted ETag.
-			if bkPartInfo, ok := partsMap[strconv.Itoa(part.PartNumber)]; ok {
-				bkETag := tryDecryptETag(objectEncryptionKey, bkPartInfo.ETag, ssec)
-				if bkETag != part.ETag {
-					writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrInvalidPart), r.URL)
-					return
-				}
-				part.ETag = bkPartInfo.ETag
-			}
-		}
-		completeParts = append(completeParts, part)
-	}
-
-	// Calculate s3 compatible md5sum for complete multipart.
-	s3MD5 := getCompleteMultipartMD5(originalCompleteParts)
-
 	completeMultiPartUpload := objectAPI.CompleteMultipartUpload
 	if api.CacheAPI() != nil {
 		completeMultiPartUpload = api.CacheAPI().CompleteMultipartUpload
@@ -3277,14 +3225,68 @@ func (api objectAPIHandlers) CompleteMultipartUploadHandler(w http.ResponseWrite
 		return
 	}
 
-	// preserve ETag if set, or set from parts.
+	// First, we compute the ETag of the multipart object.
-	if _, ok := opts.UserDefined["etag"]; !ok {
+	// The ETag of a multi-part object is always:
-		opts.UserDefined["etag"] = s3MD5
+	//   ETag := MD5(ETag_p1, ETag_p2, ...)+"-N"   (N being the number of parts)
+	//
+	// This is independent of encryption. An encrypted multipart
+	// object also has an ETag that is the MD5 of its part ETags.
+	// The fact the in case of encryption the ETag of a part is
+	// not the MD5 of the part content does not change that.
+	var completeETags []etag.ETag
+	for _, part := range complMultipartUpload.Parts {
+		ETag, err := etag.Parse(part.ETag)
+		if err != nil {
+			continue
+		}
+		completeETags = append(completeETags, ETag)
+	}
+	multipartETag := etag.Multipart(completeETags...)
+	opts.UserDefined["etag"] = multipartETag.String()
+
+	// However, in case of encryption, the persisted part ETags don't match
+	// what we have sent to the client during PutObjectPart. The reason is
+	// that ETags are encrypted. Hence, the client will send a list of complete
+	// part ETags of which non can match the ETag of any part. For example
+	//   ETag (client):          30902184f4e62dd8f98f0aaff810c626
+	//   ETag (server-internal): 20000f00ce5dc16e3f3b124f586ae1d88e9caa1c598415c2759bbb50e84a59f630902184f4e62dd8f98f0aaff810c626
+	//
+	// Therefore, we adjust all ETags sent by the client to match what is stored
+	// on the backend.
+	if objectAPI.IsEncryptionSupported() {
+		mi, err := objectAPI.GetMultipartInfo(ctx, bucket, object, uploadID, ObjectOptions{})
+		if err != nil {
+			writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
+			return
+		}
+
+		if _, ok := crypto.IsEncrypted(mi.UserDefined); ok {
+			const MaxParts = 10000
+			listPartsInfo, err := objectAPI.ListObjectParts(ctx, bucket, object, uploadID, 0, MaxParts, ObjectOptions{})
+			if err != nil {
+				writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
+				return
+			}
+			sort.Slice(listPartsInfo.Parts, func(i, j int) bool {
+				return listPartsInfo.Parts[i].PartNumber < listPartsInfo.Parts[j].PartNumber
+			})
+			sort.Slice(complMultipartUpload.Parts, func(i, j int) bool {
+				return complMultipartUpload.Parts[i].PartNumber < complMultipartUpload.Parts[j].PartNumber
+			})
+			for i := range listPartsInfo.Parts {
+				for j := range complMultipartUpload.Parts {
+					if listPartsInfo.Parts[i].PartNumber == complMultipartUpload.Parts[j].PartNumber {
+						complMultipartUpload.Parts[j].ETag = listPartsInfo.Parts[i].ETag
+						continue
+					}
+				}
+			}
+		}
 	}
 
 	w = &whiteSpaceWriter{ResponseWriter: w, Flusher: w.(http.Flusher)}
 	completeDoneCh := sendWhiteSpace(w)
-	objInfo, err := completeMultiPartUpload(ctx, bucket, object, uploadID, completeParts, opts)
+	objInfo, err := completeMultiPartUpload(ctx, bucket, object, uploadID, complMultipartUpload.Parts, opts)
 	// Stop writing white spaces to the client. Note that close(doneCh) style is not used as it
 	// can cause white space to be written after we send XML response in a race condition.
 	headerWritten := <-completeDoneCh