registry/{storage,handlers}: limit content sizes

Under certain circumstances, the use of `StorageDriver.GetContent` can
result in unbounded memory allocations. In particualr, this happens when
accessing a layer through the manifests endpoint.

This problem is mitigated by setting a 4MB limit when using to access
content that may have been accepted from a user. In practice, this means
setting the limit with the use of `BlobProvider.Get` by wrapping
`StorageDriver.GetContent` in a helper that uses `StorageDriver.Reader`
with a `limitReader` that returns an error.

When mitigating this security issue, we also noticed that the size of
manifests uploaded to the registry is also unlimited. We apply similar
logic to the request body of payloads that are full buffered.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

registry/handlers/blobupload.go

@@ -179,8 +179,8 @@ func (buh *blobUploadHandler) PatchBlobData(w http.ResponseWriter, r *http.Reque
 
 	// TODO(dmcgowan): support Content-Range header to seek and write range
 
-	if err := copyFullPayload(w, r, buh.Upload, buh, "blob PATCH", &buh.Errors); err != nil {
+	if err := copyFullPayload(w, r, buh.Upload, -1, buh, "blob PATCH"); err != nil {
-		// copyFullPayload reports the error if necessary
+		buh.Errors = append(buh.Errors, errcode.ErrorCodeUnknown.WithDetail(err.Error()))
 		return
 	}
 
@@ -218,8 +218,8 @@ func (buh *blobUploadHandler) PutBlobUploadComplete(w http.ResponseWriter, r *ht
 		return
 	}
 
-	if err := copyFullPayload(w, r, buh.Upload, buh, "blob PUT", &buh.Errors); err != nil {
+	if err := copyFullPayload(w, r, buh.Upload, -1, buh, "blob PUT"); err != nil {
-		// copyFullPayload reports the error if necessary
+		buh.Errors = append(buh.Errors, errcode.ErrorCodeUnknown.WithDetail(err.Error()))
 		return
 	}
 

registry/handlers/helpers.go

@@ -6,7 +6,6 @@ import (
 	"net/http"
 
 	ctxu "github.com/docker/distribution/context"
-	"github.com/docker/distribution/registry/api/errcode"
 )
 
 // closeResources closes all the provided resources after running the target
@@ -23,7 +22,9 @@ func closeResources(handler http.Handler, closers ...io.Closer) http.Handler {
 // copyFullPayload copies the payload of an HTTP request to destWriter. If it
 // receives less content than expected, and the client disconnected during the
 // upload, it avoids sending a 400 error to keep the logs cleaner.
-func copyFullPayload(responseWriter http.ResponseWriter, r *http.Request, destWriter io.Writer, context ctxu.Context, action string, errSlice *errcode.Errors) error {
+//
+// The copy will be limited to `limit` bytes, if limit is greater than zero.
+func copyFullPayload(responseWriter http.ResponseWriter, r *http.Request, destWriter io.Writer, limit int64, context ctxu.Context, action string) error {
 	// Get a channel that tells us if the client disconnects
 	var clientClosed <-chan bool
 	if notifier, ok := responseWriter.(http.CloseNotifier); ok {
@@ -32,8 +33,13 @@ func copyFullPayload(responseWriter http.ResponseWriter, r *http.Request, destWr
 		ctxu.GetLogger(context).Warnf("the ResponseWriter does not implement CloseNotifier (type: %T)", responseWriter)
 	}
 
+	var body = r.Body
+	if limit > 0 {
+		body = http.MaxBytesReader(responseWriter, body, limit)
+	}
+
 	// Read in the data, if any.
-	copied, err := io.Copy(destWriter, r.Body)
+	copied, err := io.Copy(destWriter, body)
 	if clientClosed != nil && (err != nil || (r.ContentLength > 0 && copied < r.ContentLength)) {
 		// Didn't receive as much content as expected. Did the client
 		// disconnect during the request? If so, avoid returning a 400
@@ -58,7 +64,6 @@ func copyFullPayload(responseWriter http.ResponseWriter, r *http.Request, destWr
 
 	if err != nil {
 		ctxu.GetLogger(context).Errorf("unknown error reading request payload: %v", err)
-		*errSlice = append(*errSlice, errcode.ErrorCodeUnknown.WithDetail(err))
 		return err
 	}
 

registry/handlers/manifests.go

@@ -22,8 +22,9 @@ import (
 // These constants determine which architecture and OS to choose from a
 // manifest list when downconverting it to a schema1 manifest.
 const (
-	defaultArch = "amd64"
+	defaultArch         = "amd64"
-	defaultOS   = "linux"
+	defaultOS           = "linux"
+	maxManifestBodySize = 4 << 20
 )
 
 // manifestDispatcher takes the request context and builds the
@@ -259,8 +260,9 @@ func (imh *manifestHandler) PutManifest(w http.ResponseWriter, r *http.Request)
 	}
 
 	var jsonBuf bytes.Buffer
-	if err := copyFullPayload(w, r, &jsonBuf, imh, "image manifest PUT", &imh.Errors); err != nil {
+	if err := copyFullPayload(w, r, &jsonBuf, maxManifestBodySize, imh, "image manifest PUT"); err != nil {
 		// copyFullPayload reports the error if necessary
+		imh.Errors = append(imh.Errors, v2.ErrorCodeManifestInvalid.WithDetail(err.Error()))
 		return
 	}
 

registry/storage/blobstore.go

@@ -27,7 +27,7 @@ func (bs *blobStore) Get(ctx context.Context, dgst digest.Digest) ([]byte, error
 		return nil, err
 	}
 
-	p, err := bs.driver.GetContent(ctx, bp)
+	p, err := getContent(ctx, bs.driver, bp)
 	if err != nil {
 		switch err.(type) {
 		case driver.PathNotFoundError:
@@ -37,7 +37,7 @@ func (bs *blobStore) Get(ctx context.Context, dgst digest.Digest) ([]byte, error
 		return nil, err
 	}
 
-	return p, err
+	return p, nil
 }
 
 func (bs *blobStore) Open(ctx context.Context, dgst digest.Digest) (distribution.ReadSeekCloser, error) {

registry/storage/io.go

@@ -0,0 +1,71 @@
+package storage
+
+import (
+	"errors"
+	"io"
+	"io/ioutil"
+
+	"github.com/docker/distribution/context"
+	"github.com/docker/distribution/registry/storage/driver"
+)
+
+const (
+	maxBlobGetSize = 4 << 20
+)
+
+func getContent(ctx context.Context, driver driver.StorageDriver, p string) ([]byte, error) {
+	r, err := driver.Reader(ctx, p, 0)
+	if err != nil {
+		return nil, err
+	}
+
+	return readAllLimited(r, maxBlobGetSize)
+}
+
+func readAllLimited(r io.Reader, limit int64) ([]byte, error) {
+	r = limitReader(r, limit)
+	return ioutil.ReadAll(r)
+}
+
+// limitReader returns a new reader limited to n bytes. Unlike io.LimitReader,
+// this returns an error when the limit reached.
+func limitReader(r io.Reader, n int64) io.Reader {
+	return &limitedReader{r: r, n: n}
+}
+
+// limitedReader implements a reader that errors when the limit is reached.
+//
+// Partially cribbed from net/http.MaxBytesReader.
+type limitedReader struct {
+	r   io.Reader // underlying reader
+	n   int64     // max bytes remaining
+	err error     // sticky error
+}
+
+func (l *limitedReader) Read(p []byte) (n int, err error) {
+	if l.err != nil {
+		return 0, l.err
+	}
+	if len(p) == 0 {
+		return 0, nil
+	}
+	// If they asked for a 32KB byte read but only 5 bytes are
+	// remaining, no need to read 32KB. 6 bytes will answer the
+	// question of the whether we hit the limit or go past it.
+	if int64(len(p)) > l.n+1 {
+		p = p[:l.n+1]
+	}
+	n, err = l.r.Read(p)
+
+	if int64(n) <= l.n {
+		l.n -= int64(n)
+		l.err = err
+		return n, err
+	}
+
+	n = int(l.n)
+	l.n = 0
+
+	l.err = errors.New("storage: read exceeds limit")
+	return n, l.err
+}