s3: Fix precondition failed in CopyObjectPart when src is encrypted (#7276)

CopyObject precondition checks into GetObjectReader
in order to perform SSE-C pre-condition checks using the
last 32 bytes of encrypted ETag rather than the decrypted
ETag

This also necessitates moving precondition checks for
gateways to gateway layer rather than object handler check

cmd/disk-cache.go

@@ -254,8 +254,7 @@ func (c cacheObjects) GetObjectNInfo(ctx context.Context, bucket, object string,
 
 	cleanupBackend := func() { bkReader.Close() }
 	cleanupPipe := func() { pipeReader.Close() }
-	gr = NewGetObjectReaderFromReader(teeReader, bkReader.ObjInfo, cleanupBackend, cleanupPipe)
+	return NewGetObjectReaderFromReader(teeReader, bkReader.ObjInfo, opts.CheckCopyPrecondFn, cleanupBackend, cleanupPipe)
-	return gr, nil
 }
 
 // Uses cached-object to serve the request. If object is not cached it serves the request from the backend and also

cmd/fs-v1.go

@@ -499,7 +499,7 @@ func (fs *FSObjects) GetObjectNInfo(ctx context.Context, bucket, object string,
 	if hasSuffix(object, slashSeparator) {
 		// The lock taken above is released when
 		// objReader.Close() is called by the caller.
-		return NewGetObjectReaderFromReader(bytes.NewBuffer(nil), objInfo, nsUnlocker), nil
+		return NewGetObjectReaderFromReader(bytes.NewBuffer(nil), objInfo, opts.CheckCopyPrecondFn, nsUnlocker)
 	}
 	// Take a rwPool lock for NFS gateway type deployment
 	rwPoolUnlocker := func() {}
@@ -516,7 +516,7 @@ func (fs *FSObjects) GetObjectNInfo(ctx context.Context, bucket, object string,
 		rwPoolUnlocker = func() { fs.rwPool.Close(fsMetaPath) }
 	}
 
-	objReaderFn, off, length, rErr := NewGetObjectReader(rs, objInfo, nsUnlocker, rwPoolUnlocker)
+	objReaderFn, off, length, rErr := NewGetObjectReader(rs, objInfo, opts.CheckCopyPrecondFn, nsUnlocker, rwPoolUnlocker)
 	if rErr != nil {
 		return nil, rErr
 	}
@@ -544,7 +544,7 @@ func (fs *FSObjects) GetObjectNInfo(ctx context.Context, bucket, object string,
 		return nil, err
 	}
 
-	return objReaderFn(reader, h, closeFn)
+	return objReaderFn(reader, h, opts.CheckCopyPrecondFn, closeFn)
 }
 
 // GetObject - reads an object from the disk.

cmd/gateway/azure/gateway-azure.go

@@ -651,7 +651,7 @@ func (a *azureObjects) GetObjectNInfo(ctx context.Context, bucket, object string
 	// Setup cleanup function to cause the above go-routine to
 	// exit in case of partial read
 	pipeCloser := func() { pr.Close() }
-	return minio.NewGetObjectReaderFromReader(pr, objInfo, pipeCloser), nil
+	return minio.NewGetObjectReaderFromReader(pr, objInfo, opts.CheckCopyPrecondFn, pipeCloser)
 }
 
 // GetObject - reads an object from azure. Supports additional
@@ -829,6 +829,9 @@ func (a *azureObjects) PutObject(ctx context.Context, bucket, object string, r *
 // CopyObject - Copies a blob from source container to destination container.
 // Uses Azure equivalent CopyBlob API.
 func (a *azureObjects) CopyObject(ctx context.Context, srcBucket, srcObject, destBucket, destObject string, srcInfo minio.ObjectInfo, srcOpts, dstOpts minio.ObjectOptions) (objInfo minio.ObjectInfo, err error) {
+	if srcOpts.CheckCopyPrecondFn != nil && srcOpts.CheckCopyPrecondFn(srcInfo, "") {
+		return minio.ObjectInfo{}, minio.PreConditionFailed{}
+	}
 	srcBlobURL := a.client.GetContainerReference(srcBucket).GetBlobReference(srcObject).GetURL()
 	destBlob := a.client.GetContainerReference(destBucket).GetBlobReference(destObject)
 	azureMeta, props, err := s3MetaToAzureProperties(ctx, srcInfo.UserDefined)

cmd/gateway/b2/gateway-b2.go

@@ -417,7 +417,7 @@ func (l *b2Objects) GetObjectNInfo(ctx context.Context, bucket, object string, r
 	// Setup cleanup function to cause the above go-routine to
 	// exit in case of partial read
 	pipeCloser := func() { pr.Close() }
-	return minio.NewGetObjectReaderFromReader(pr, objInfo, pipeCloser), nil
+	return minio.NewGetObjectReaderFromReader(pr, objInfo, opts.CheckCopyPrecondFn, pipeCloser)
 }
 
 // GetObject reads an object from B2. Supports additional

cmd/gateway/gcs/gateway-gcs.go

@@ -753,7 +753,7 @@ func (l *gcsGateway) GetObjectNInfo(ctx context.Context, bucket, object string,
 	// Setup cleanup function to cause the above go-routine to
 	// exit in case of partial read
 	pipeCloser := func() { pr.Close() }
-	return minio.NewGetObjectReaderFromReader(pr, objInfo, pipeCloser), nil
+	return minio.NewGetObjectReaderFromReader(pr, objInfo, opts.CheckCopyPrecondFn, pipeCloser)
 }
 
 // GetObject - reads an object from GCS. Supports additional
@@ -929,7 +929,9 @@ func (l *gcsGateway) PutObject(ctx context.Context, bucket string, key string, r
 // CopyObject - Copies a blob from source container to destination container.
 func (l *gcsGateway) CopyObject(ctx context.Context, srcBucket string, srcObject string, destBucket string, destObject string,
 	srcInfo minio.ObjectInfo, srcOpts, dstOpts minio.ObjectOptions) (minio.ObjectInfo, error) {
-
+	if srcOpts.CheckCopyPrecondFn != nil && srcOpts.CheckCopyPrecondFn(srcInfo, "") {
+		return minio.ObjectInfo{}, minio.PreConditionFailed{}
+	}
 	src := l.client.Bucket(srcBucket).Object(srcObject)
 	dst := l.client.Bucket(destBucket).Object(destObject)
 

cmd/gateway/oss/gateway-oss.go

@@ -26,7 +26,7 @@ import (
 	"strings"
 
 	"github.com/aliyun/aliyun-oss-go-sdk/oss"
-	"github.com/dustin/go-humanize"
+	humanize "github.com/dustin/go-humanize"
 
 	"github.com/minio/cli"
 	miniogopolicy "github.com/minio/minio-go/pkg/policy"
@@ -570,7 +570,7 @@ func (l *ossObjects) GetObjectNInfo(ctx context.Context, bucket, object string,
 	// Setup cleanup function to cause the above go-routine to
 	// exit in case of partial read
 	pipeCloser := func() { pr.Close() }
-	return minio.NewGetObjectReaderFromReader(pr, objInfo, pipeCloser), nil
+	return minio.NewGetObjectReaderFromReader(pr, objInfo, opts.CheckCopyPrecondFn, pipeCloser)
 }
 
 // GetObject reads an object on OSS. Supports additional
@@ -665,6 +665,9 @@ func (l *ossObjects) PutObject(ctx context.Context, bucket, object string, r *mi
 
 // CopyObject copies an object from source bucket to a destination bucket.
 func (l *ossObjects) CopyObject(ctx context.Context, srcBucket, srcObject, dstBucket, dstObject string, srcInfo minio.ObjectInfo, srcOpts, dstOpts minio.ObjectOptions) (objInfo minio.ObjectInfo, err error) {
+	if srcOpts.CheckCopyPrecondFn != nil && srcOpts.CheckCopyPrecondFn(srcInfo, "") {
+		return minio.ObjectInfo{}, minio.PreConditionFailed{}
+	}
 	bkt, err := l.Client.Bucket(srcBucket)
 	if err != nil {
 		logger.LogIf(ctx, err)

cmd/gateway/s3/gateway-s3-sse.go

@@ -313,7 +313,7 @@ func (l *s3EncObjects) GetObjectNInfo(ctx context.Context, bucket, object string
 		return l.s3Objects.GetObjectNInfo(ctx, bucket, object, rs, h, lockType, opts)
 	}
 	objInfo.UserDefined = minio.CleanMinioInternalMetadataKeys(objInfo.UserDefined)
-	fn, off, length, err := minio.NewGetObjectReader(rs, objInfo)
+	fn, off, length, err := minio.NewGetObjectReader(rs, objInfo, o.CheckCopyPrecondFn)
 	if err != nil {
 		return nil, minio.ErrorRespToObjectError(err)
 	}
@@ -329,7 +329,7 @@ func (l *s3EncObjects) GetObjectNInfo(ctx context.Context, bucket, object string
 	// Setup cleanup function to cause the above go-routine to
 	// exit in case of partial read
 	pipeCloser := func() { pr.Close() }
-	return fn(pr, h, pipeCloser)
+	return fn(pr, h, o.CheckCopyPrecondFn, pipeCloser)
 }
 
 // GetObjectInfo reads object info and replies back ObjectInfo

cmd/gateway/s3/gateway-s3.go

@@ -400,7 +400,7 @@ func (l *s3Objects) GetObjectNInfo(ctx context.Context, bucket, object string, r
 	// Setup cleanup function to cause the above go-routine to
 	// exit in case of partial read
 	pipeCloser := func() { pr.Close() }
-	return minio.NewGetObjectReaderFromReader(pr, objInfo, pipeCloser), nil
+	return minio.NewGetObjectReaderFromReader(pr, objInfo, opts.CheckCopyPrecondFn, pipeCloser)
 }
 
 // GetObject reads an object from S3. Supports additional
@@ -463,6 +463,9 @@ func (l *s3Objects) PutObject(ctx context.Context, bucket string, object string,
 
 // CopyObject copies an object from source bucket to a destination bucket.
 func (l *s3Objects) CopyObject(ctx context.Context, srcBucket string, srcObject string, dstBucket string, dstObject string, srcInfo minio.ObjectInfo, srcOpts, dstOpts minio.ObjectOptions) (objInfo minio.ObjectInfo, err error) {
+	if srcOpts.CheckCopyPrecondFn != nil && srcOpts.CheckCopyPrecondFn(srcInfo, "") {
+		return minio.ObjectInfo{}, minio.PreConditionFailed{}
+	}
 	// Set this header such that following CopyObject() always sets the right metadata on the destination.
 	// metadata input is already a trickled down value from interpreting x-amz-metadata-directive at
 	// handler layer. So what we have right now is supposed to be applied on the destination object anyways.
@@ -533,6 +536,9 @@ func (l *s3Objects) PutObjectPart(ctx context.Context, bucket string, object str
 // existing object or a part of it.
 func (l *s3Objects) CopyObjectPart(ctx context.Context, srcBucket, srcObject, destBucket, destObject, uploadID string,
 	partID int, startOffset, length int64, srcInfo minio.ObjectInfo, srcOpts, dstOpts minio.ObjectOptions) (p minio.PartInfo, err error) {
+	if srcOpts.CheckCopyPrecondFn != nil && srcOpts.CheckCopyPrecondFn(srcInfo, "") {
+		return minio.PartInfo{}, minio.PreConditionFailed{}
+	}
 	srcInfo.UserDefined = map[string]string{
 		"x-amz-copy-source-if-match": srcInfo.ETag,
 	}

cmd/object-api-errors.go

@@ -383,3 +383,15 @@ func isErrObjectNotFound(err error) bool {
 	_, ok := err.(ObjectNotFound)
 	return ok
 }
+
+// PreConditionFailed - Check if copy precondition failed
+type PreConditionFailed struct{}
+
+func (e PreConditionFailed) Error() string {
+	return "At least one of the pre-conditions you specified did not hold"
+}
+
+func isErrPreconditionFailed(err error) bool {
+	_, ok := err.(PreConditionFailed)
+	return ok
+}

cmd/object-api-interface.go

@@ -26,10 +26,14 @@ import (
 	"github.com/minio/minio/pkg/policy"
 )
 
+// CheckCopyPreconditionFn returns true if copy precondition check failed.
+type CheckCopyPreconditionFn func(o ObjectInfo, encETag string) bool
+
 // ObjectOptions represents object options for ObjectLayer operations
 type ObjectOptions struct {
 	ServerSideEncryption encrypt.ServerSide
 	UserDefined          map[string]string
+	CheckCopyPrecondFn   CheckCopyPreconditionFn
 }
 
 // LockType represents required locking for ObjectLayer operations

cmd/object-api-utils.go

@@ -429,30 +429,41 @@ type GetObjectReader struct {
 	pReader io.Reader
 
 	cleanUpFns []func()
+	precondFn  func(ObjectInfo, string) bool
 	once       sync.Once
 }
 
 // NewGetObjectReaderFromReader sets up a GetObjectReader with a given
 // reader. This ignores any object properties.
-func NewGetObjectReaderFromReader(r io.Reader, oi ObjectInfo, cleanupFns ...func()) *GetObjectReader {
+func NewGetObjectReaderFromReader(r io.Reader, oi ObjectInfo, pcfn CheckCopyPreconditionFn, cleanupFns ...func()) (*GetObjectReader, error) {
+	if pcfn != nil {
+		if ok := pcfn(oi, ""); ok {
+			// Call the cleanup funcs
+			for i := len(cleanupFns) - 1; i >= 0; i-- {
+				cleanupFns[i]()
+			}
+			return nil, PreConditionFailed{}
+		}
+	}
 	return &GetObjectReader{
 		ObjInfo:    oi,
 		pReader:    r,
 		cleanUpFns: cleanupFns,
-	}
+		precondFn:  pcfn,
+	}, nil
 }
 
 // ObjReaderFn is a function type that takes a reader and returns
 // GetObjectReader and an error. Request headers are passed to provide
 // encryption parameters. cleanupFns allow cleanup funcs to be
 // registered for calling after usage of the reader.
-type ObjReaderFn func(inputReader io.Reader, h http.Header, cleanupFns ...func()) (r *GetObjectReader, err error)
+type ObjReaderFn func(inputReader io.Reader, h http.Header, pcfn CheckCopyPreconditionFn, cleanupFns ...func()) (r *GetObjectReader, err error)
 
 // NewGetObjectReader creates a new GetObjectReader. The cleanUpFns
 // are called on Close() in reverse order as passed here. NOTE: It is
 // assumed that clean up functions do not panic (otherwise, they may
 // not all run!).
-func NewGetObjectReader(rs *HTTPRangeSpec, oi ObjectInfo, cleanUpFns ...func()) (
+func NewGetObjectReader(rs *HTTPRangeSpec, oi ObjectInfo, pcfn CheckCopyPreconditionFn, cleanUpFns ...func()) (
 	fn ObjReaderFn, off, length int64, err error) {
 
 	// Call the clean-up functions immediately in case of exit
@@ -493,7 +504,7 @@ func NewGetObjectReader(rs *HTTPRangeSpec, oi ObjectInfo, cleanUpFns ...func())
 		// a reader that returns the desired range of
 		// encrypted bytes. The header parameter is used to
 		// provide encryption parameters.
-		fn = func(inputReader io.Reader, h http.Header, cFns ...func()) (r *GetObjectReader, err error) {
+		fn = func(inputReader io.Reader, h http.Header, pcfn CheckCopyPreconditionFn, cFns ...func()) (r *GetObjectReader, err error) {
 			copySource := h.Get(crypto.SSECopyAlgorithm) != ""
 
 			cFns = append(cleanUpFns, cFns...)
@@ -508,9 +519,18 @@ func NewGetObjectReader(rs *HTTPRangeSpec, oi ObjectInfo, cleanUpFns ...func())
 				}
 				return nil, err
 			}
+			encETag := oi.ETag
+			oi.ETag = getDecryptedETag(h, oi, copySource) // Decrypt the ETag before top layer consumes this value.
 
-			// Decrypt the ETag before top layer consumes this value.
+			if pcfn != nil {
-			oi.ETag = getDecryptedETag(h, oi, copySource)
+				if ok := pcfn(oi, encETag); ok {
+					// Call the cleanup funcs
+					for i := len(cFns) - 1; i >= 0; i-- {
+						cFns[i]()
+					}
+					return nil, PreConditionFailed{}
+				}
+			}
 
 			// Apply the skipLen and limit on the
 			// decrypted stream
@@ -521,6 +541,7 @@ func NewGetObjectReader(rs *HTTPRangeSpec, oi ObjectInfo, cleanUpFns ...func())
 				ObjInfo:    oi,
 				pReader:    decReader,
 				cleanUpFns: cFns,
+				precondFn:  pcfn,
 			}
 			return r, nil
 		}
@@ -552,7 +573,17 @@ func NewGetObjectReader(rs *HTTPRangeSpec, oi ObjectInfo, cleanUpFns ...func())
 				return nil, 0, 0, errInvalidRange
 			}
 		}
-		fn = func(inputReader io.Reader, _ http.Header, cFns ...func()) (r *GetObjectReader, err error) {
+		fn = func(inputReader io.Reader, _ http.Header, pcfn CheckCopyPreconditionFn, cFns ...func()) (r *GetObjectReader, err error) {
+			cFns = append(cleanUpFns, cFns...)
+			if pcfn != nil {
+				if ok := pcfn(oi, ""); ok {
+					// Call the cleanup funcs
+					for i := len(cFns) - 1; i >= 0; i-- {
+						cFns[i]()
+					}
+					return nil, PreConditionFailed{}
+				}
+			}
 			// Decompression reader.
 			snappyReader := snappy.NewReader(inputReader)
 			// Apply the skipLen and limit on the
@@ -564,7 +595,8 @@ func NewGetObjectReader(rs *HTTPRangeSpec, oi ObjectInfo, cleanUpFns ...func())
 			r = &GetObjectReader{
 				ObjInfo:    oi,
 				pReader:    decReader,
-				cleanUpFns: append(cleanUpFns, cFns...),
+				cleanUpFns: cFns,
+				precondFn:  pcfn,
 			}
 			return r, nil
 		}
@@ -574,11 +606,22 @@ func NewGetObjectReader(rs *HTTPRangeSpec, oi ObjectInfo, cleanUpFns ...func())
 		if err != nil {
 			return nil, 0, 0, err
 		}
-		fn = func(inputReader io.Reader, _ http.Header, cFns ...func()) (r *GetObjectReader, err error) {
+		fn = func(inputReader io.Reader, _ http.Header, pcfn CheckCopyPreconditionFn, cFns ...func()) (r *GetObjectReader, err error) {
+			cFns = append(cleanUpFns, cFns...)
+			if pcfn != nil {
+				if ok := pcfn(oi, ""); ok {
+					// Call the cleanup funcs
+					for i := len(cFns) - 1; i >= 0; i-- {
+						cFns[i]()
+					}
+					return nil, PreConditionFailed{}
+				}
+			}
 			r = &GetObjectReader{
 				ObjInfo:    oi,
 				pReader:    inputReader,
-				cleanUpFns: append(cleanUpFns, cFns...),
+				cleanUpFns: cFns,
+				precondFn:  pcfn,
 			}
 			return r, nil
 		}

cmd/object-handlers-common.go

@@ -23,6 +23,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/minio/minio/cmd/crypto"
 	"github.com/minio/minio/pkg/event"
 	"github.com/minio/minio/pkg/handlers"
 )
@@ -33,8 +34,8 @@ import (
 //  x-amz-copy-source-if-unmodified-since
 //  x-amz-copy-source-if-match
 //  x-amz-copy-source-if-none-match
-func checkCopyObjectPartPreconditions(ctx context.Context, w http.ResponseWriter, r *http.Request, objInfo ObjectInfo) bool {
+func checkCopyObjectPartPreconditions(ctx context.Context, w http.ResponseWriter, r *http.Request, objInfo ObjectInfo, encETag string) bool {
-	return checkCopyObjectPreconditions(ctx, w, r, objInfo)
+	return checkCopyObjectPreconditions(ctx, w, r, objInfo, encETag)
 }
 
 // Validates the preconditions for CopyObject, returns true if CopyObject operation should not proceed.
@@ -43,11 +44,14 @@ func checkCopyObjectPartPreconditions(ctx context.Context, w http.ResponseWriter
 //  x-amz-copy-source-if-unmodified-since
 //  x-amz-copy-source-if-match
 //  x-amz-copy-source-if-none-match
-func checkCopyObjectPreconditions(ctx context.Context, w http.ResponseWriter, r *http.Request, objInfo ObjectInfo) bool {
+func checkCopyObjectPreconditions(ctx context.Context, w http.ResponseWriter, r *http.Request, objInfo ObjectInfo, encETag string) bool {
 	// Return false for methods other than GET and HEAD.
 	if r.Method != "PUT" {
 		return false
 	}
+	if encETag == "" {
+		encETag = objInfo.ETag
+	}
 	// If the object doesn't have a modtime (IsZero), or the modtime
 	// is obviously garbage (Unix time == 0), then ignore modtimes
 	// and don't process the If-Modified-Since header.
@@ -95,11 +99,16 @@ func checkCopyObjectPreconditions(ctx context.Context, w http.ResponseWriter, r
 		}
 	}
 
+	ssec := crypto.SSECopy.IsRequested(r.Header)
 	// x-amz-copy-source-if-match : Return the object only if its entity tag (ETag) is the
 	// same as the one specified; otherwise return a 412 (precondition failed).
 	ifMatchETagHeader := r.Header.Get("x-amz-copy-source-if-match")
 	if ifMatchETagHeader != "" {
-		if objInfo.ETag != "" && !isETagEqual(objInfo.ETag, ifMatchETagHeader) {
+		etag := objInfo.ETag
+		if ssec {
+			etag = encETag[len(encETag)-32:]
+		}
+		if objInfo.ETag != "" && !isETagEqual(etag, ifMatchETagHeader) {
 			// If the object ETag does not match with the specified ETag.
 			writeHeaders()
 			writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrPreconditionFailed), r.URL, guessIsBrowserReq(r))
@@ -111,7 +120,11 @@ func checkCopyObjectPreconditions(ctx context.Context, w http.ResponseWriter, r
 	// one specified otherwise, return a 304 (not modified).
 	ifNoneMatchETagHeader := r.Header.Get("x-amz-copy-source-if-none-match")
 	if ifNoneMatchETagHeader != "" {
-		if objInfo.ETag != "" && isETagEqual(objInfo.ETag, ifNoneMatchETagHeader) {
+		etag := objInfo.ETag
+		if ssec {
+			etag = encETag[len(encETag)-32:]
+		}
+		if objInfo.ETag != "" && isETagEqual(etag, ifNoneMatchETagHeader) {
 			// If the object ETag matches with the specified ETag.
 			writeHeaders()
 			writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrPreconditionFailed), r.URL, guessIsBrowserReq(r))

cmd/object-handlers.go

@@ -760,21 +760,23 @@ func (api objectAPIHandlers) CopyObjectHandler(w http.ResponseWriter, r *http.Re
 	if !cpSrcDstSame {
 		lock = readLock
 	}
-
+	checkCopyPrecondFn := func(o ObjectInfo, encETag string) bool {
+		return checkCopyObjectPreconditions(ctx, w, r, o, encETag)
+	}
+	getOpts.CheckCopyPrecondFn = checkCopyPrecondFn
+	srcOpts.CheckCopyPrecondFn = checkCopyPrecondFn
 	var rs *HTTPRangeSpec
 	gr, err := getObjectNInfo(ctx, srcBucket, srcObject, rs, r.Header, lock, getOpts)
 	if err != nil {
+		if isErrPreconditionFailed(err) {
+			return
+		}
 		writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL, guessIsBrowserReq(r))
 		return
 	}
 	defer gr.Close()
 	srcInfo := gr.ObjInfo
 
-	// Verify before x-amz-copy-source preconditions before continuing with CopyObject.
-	if checkCopyObjectPreconditions(ctx, w, r, srcInfo) {
-		return
-	}
-
 	/// maximum Upload size for object in a single CopyObject operation.
 	if isMaxObjectSize(srcInfo.Size) {
 		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrEntityTooLarge), r.URL, guessIsBrowserReq(r))
@@ -1573,9 +1575,17 @@ func (api objectAPIHandlers) CopyObjectPartHandler(w http.ResponseWriter, r *htt
 
 		}
 	}
+	checkCopyPartPrecondFn := func(o ObjectInfo, encETag string) bool {
+		return checkCopyObjectPartPreconditions(ctx, w, r, o, encETag)
+	}
+	getOpts.CheckCopyPrecondFn = checkCopyPartPrecondFn
+	srcOpts.CheckCopyPrecondFn = checkCopyPartPrecondFn
 
 	gr, err := getObjectNInfo(ctx, srcBucket, srcObject, rs, r.Header, readLock, getOpts)
 	if err != nil {
+		if isErrPreconditionFailed(err) {
+			return
+		}
 		writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL, guessIsBrowserReq(r))
 		return
 	}
@@ -1597,11 +1607,6 @@ func (api objectAPIHandlers) CopyObjectPartHandler(w http.ResponseWriter, r *htt
 		return
 	}
 
-	// Verify before x-amz-copy-source preconditions before continuing with CopyObject.
-	if checkCopyObjectPartPreconditions(ctx, w, r, srcInfo) {
-		return
-	}
-
 	// Get the object offset & length
 	startOffset, length, err := rs.GetOffsetLength(actualPartSize)
 	if err != nil {

cmd/xl-v1-object.go

@@ -182,7 +182,7 @@ func (xl xlObjects) GetObjectNInfo(ctx context.Context, bucket, object string, r
 			nsUnlocker()
 			return nil, toObjectErr(err, bucket, object)
 		}
-		return NewGetObjectReaderFromReader(bytes.NewBuffer(nil), objInfo, nsUnlocker), nil
+		return NewGetObjectReaderFromReader(bytes.NewBuffer(nil), objInfo, opts.CheckCopyPrecondFn, nsUnlocker)
 	}
 
 	var objInfo ObjectInfo
@@ -192,7 +192,7 @@ func (xl xlObjects) GetObjectNInfo(ctx context.Context, bucket, object string, r
 		return nil, toObjectErr(err, bucket, object)
 	}
 
-	fn, off, length, nErr := NewGetObjectReader(rs, objInfo, nsUnlocker)
+	fn, off, length, nErr := NewGetObjectReader(rs, objInfo, opts.CheckCopyPrecondFn, nsUnlocker)
 	if nErr != nil {
 		return nil, nErr
 	}
@@ -206,7 +206,7 @@ func (xl xlObjects) GetObjectNInfo(ctx context.Context, bucket, object string, r
 	// case of incomplete read.
 	pipeCloser := func() { pr.Close() }
 
-	return fn(pr, h, pipeCloser)
+	return fn(pr, h, opts.CheckCopyPrecondFn, pipeCloser)
 }
 
 // GetObject - reads an object erasured coded across multiple