--- nono/host/diskimage.cpp	2026/04/29 17:05:00	1.1.1.2
+++ nono/host/diskimage.cpp	2026/04/29 17:05:26	1.1.1.5
@@ -36,12 +36,10 @@ DiskImage::CreateHandler(const std::stri
 	cow_enable = false;
 
 	// 今の所 Raw しかない
-	try {
-		driver.reset(new DiskImageRaw(pathname));
+	driver.reset(new DiskImageRaw(pathname));
+	if ((bool)driver) {
 		return true;
-	} catch (...) {
 	}
-
 	return false;
 }
 
@@ -91,7 +89,7 @@ DiskImage::Open(bool read_only, bool cow
 		assert(cowname.empty() == false);
 
 		cowname = gMainApp.GetVMDir() + "/." + cowname + ".cow";
-		cowfd = open(cowname.c_str(), O_RDWR | O_CREAT | O_TRUNC, 0644);
+		cowfd = open(cowname.c_str(), O_RDWR | O_CREAT | O_TRUNC, 0600);
 		if (cowfd < 0) {
 			return false;
 		}
@@ -132,7 +130,7 @@ DiskImage::Read(void *buf, off_t offset,
 {
 	assert((bool)driver);
 
-	if (__predict_false(offset + size >= GetSize())) {
+	if (__predict_false(offset + size > GetSize())) {
 		return false;
 	}
 
@@ -178,7 +176,7 @@ DiskImage::Write(const void *buf, off_t
 {
 	assert((bool)driver);
 
-	if (__predict_false(offset + size >= GetSize())) {
+	if (__predict_false(offset + size > GetSize())) {
 		return false;
 	}