Fix race in LFS ContentStore.Put(...) (#14895)

modules/lfs/content_store.go

@@ -9,6 +9,7 @@ import (
 	"encoding/hex"
 	"errors"
 	"fmt"
+	"hash"
 	"io"
 	"os"
 
@@ -66,30 +67,27 @@ func (s *ContentStore) Get(meta *models.LFSMetaObject, fromByte int64) (io.ReadC
 
 // Put takes a Meta object and an io.Reader and writes the content to the store.
 func (s *ContentStore) Put(meta *models.LFSMetaObject, r io.Reader) error {
-	hash := sha256.New()
-	rd := io.TeeReader(r, hash)
 	p := meta.RelativePath()
-	written, err := s.Save(p, rd)
+
+	// Wrap the provided reader with an inline hashing and size checker
+	wrappedRd := newHashingReader(meta.Size, meta.Oid, r)
+
+	// now pass the wrapped reader to Save - if there is a size mismatch or hash mismatch then
+	// the errors returned by the newHashingReader should percolate up to here
+	written, err := s.Save(p, wrappedRd)
 	if err != nil {
 		log.Error("Whilst putting LFS OID[%s]: Failed to copy to tmpPath: %s Error: %v", meta.Oid, p, err)
 		return err
 	}
 
+	// This shouldn't happen but it is sensible to test
 	if written != meta.Size {
 		if err := s.Delete(p); err != nil {
 			log.Error("Cleaning the LFS OID[%s] failed: %v", meta.Oid, err)
 		}
 		return errSizeMismatch
 	}
 
-	shaStr := hex.EncodeToString(hash.Sum(nil))
-	if shaStr != meta.Oid {
-		if err := s.Delete(p); err != nil {
-			log.Error("Cleaning the LFS OID[%s] failed: %v", meta.Oid, err)
-		}
-		return errHashMismatch
-	}
-
 	return nil
 }
 
@@ -118,3 +116,45 @@ func (s *ContentStore) Verify(meta *models.LFSMetaObject) (bool, error) {
 
 	return true, nil
 }
+
+type hashingReader struct {
+	internal     io.Reader
+	currentSize  int64
+	expectedSize int64
+	hash         hash.Hash
+	expectedHash string
+}
+
+func (r *hashingReader) Read(b []byte) (int, error) {
+	n, err := r.internal.Read(b)
+
+	if n > 0 {
+		r.currentSize += int64(n)
+		wn, werr := r.hash.Write(b[:n])
+		if wn != n || werr != nil {
+			return n, werr
+		}
+	}
+
+	if err != nil && err == io.EOF {
+		if r.currentSize != r.expectedSize {
+			return n, errSizeMismatch
+		}
+
+		shaStr := hex.EncodeToString(r.hash.Sum(nil))
+		if shaStr != r.expectedHash {
+			return n, errHashMismatch
+		}
+	}
+
+	return n, err
+}
+
+func newHashingReader(expectedSize int64, expectedHash string, reader io.Reader) *hashingReader {
+	return &hashingReader{
+		internal:     reader,
+		expectedSize: expectedSize,
+		expectedHash: expectedHash,
+		hash:         sha256.New(),
+	}
+}