cmd: fix limitedRead returning nil error when Stat fails

cmd/containerd-shim-lcow-v2/manager.go

@@ -260,11 +260,11 @@ func limitedRead(filePath string, readLimitBytes int64) ([]byte, error) {
 		readLimitBytes = fi.Size()
 	}
 	buf := make([]byte, readLimitBytes)
-	_, err = f.Read(buf)
-	if err != nil {
+	n, err := io.ReadFull(f, buf)
+	if err != nil && !errors.Is(err, io.ErrUnexpectedEOF) {
 		return []byte{}, fmt.Errorf("read file %s: %w", filePath, err)
 	}
-	return buf, nil
+	return buf[:n], nil
 }
 
 // Info returns runtime information about this shim including its name, version,

cmd/containerd-shim-runhcs-v1/delete.go

@@ -5,6 +5,7 @@ package main
 import (
 	"context"
 	"fmt"
+	"io"
 	"os"
 	"path/filepath"
 	"time"
@@ -30,18 +31,19 @@ func limitedRead(filePath string, readLimitBytes int64) ([]byte, error) {
 		return nil, errors.Wrapf(err, "limited read failed to open file: %s", filePath)
 	}
 	defer f.Close()
-	if fi, err := f.Stat(); err == nil {
-		if fi.Size() < readLimitBytes {
-			readLimitBytes = fi.Size()
-		}
-		buf := make([]byte, readLimitBytes)
-		_, err := f.Read(buf)
-		if err != nil {
-			return []byte{}, errors.Wrapf(err, "limited read failed during file read: %s", filePath)
-		}
-		return buf, nil
+	fi, err := f.Stat()
+	if err != nil {
+		return []byte{}, errors.Wrapf(err, "limited read failed during file stat: %s", filePath)
+	}
+	if fi.Size() < readLimitBytes {
+		readLimitBytes = fi.Size()
+	}
+	buf := make([]byte, readLimitBytes)
+	n, err := io.ReadFull(f, buf)
+	if err != nil && err != io.ErrUnexpectedEOF {
+		return []byte{}, errors.Wrapf(err, "limited read failed during file read: %s", filePath)
 	}
-	return []byte{}, errors.Wrapf(err, "limited read failed during file stat: %s", filePath)
+	return buf[:n], nil
 }
 
 var deleteCommand = cli.Command{

cmd/containerd-shim-runhcs-v1/delete_test.go

@@ -0,0 +1,44 @@
+//go:build windows
+
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// TestLimitedRead verifies that limitedRead enforces the byte limit when the
+// file is larger than the limit and reads the full content when the file is
+// smaller than the limit.
+func TestLimitedRead(t *testing.T) {
+	filePath := filepath.Join(t.TempDir(), "panic.log")
+	if err := os.WriteFile(filePath, []byte("hello"), 0o644); err != nil {
+		t.Fatalf("WriteFile: %v", err)
+	}
+
+	buf, err := limitedRead(filePath, 2)
+	if err != nil {
+		t.Fatalf("limitedRead: %v", err)
+	}
+	if string(buf) != "he" {
+		t.Fatalf("expected 'he', got %q", string(buf))
+	}
+
+	buf, err = limitedRead(filePath, 10)
+	if err != nil {
+		t.Fatalf("limitedRead: %v", err)
+	}
+	if string(buf) != "hello" {
+		t.Fatalf("expected 'hello', got %q", string(buf))
+	}
+}
+
+// TestLimitedReadMissingFile verifies that limitedRead returns an error when
+// the target file does not exist.
+func TestLimitedReadMissingFile(t *testing.T) {
+	_, err := limitedRead(filepath.Join(t.TempDir(), "missing.log"), 10)
+	if err == nil {
+		t.Fatalf("expected error for missing file")
+	}
+}