Fix race in LFS ContentStore.Put(...) (go-gitea#14895)

Backport go-gitea#14895

Continuing on from go-gitea#14888

The previous implementation has race whereby an incomplete upload or
hash mismatch upload can end up in the ContentStore. This PR moves the
validation into the reader so that if there is a hash error or size
mismatch the reader will return with an error instead of an io.EOF
causing the storage to abort the storage.

Signed-off-by: Andrew Thornton <art27@cantab.net>

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(),
+	}
+}