extmod/vfs_rom: Remove ability to create VfsRom from an address.

It's not necessary to support this, which allows an arbitrary memory
address to be specified and potentially allows invalid memory accesses.

Requiring an object with the buffer protocol is safer, and also means that
the length of the region is always specified.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

extmod/vfs_rom.c

@@ -198,15 +198,13 @@ static mp_obj_t vfs_rom_make_new(const mp_obj_type_t *type, size_t n_args, size_
     self->base.type = type;
     self->memory = args[0];
 
+    // Get the ROMFS memory region.
     mp_buffer_info_t bufinfo;
-    if (mp_get_buffer(self->memory, &bufinfo, MP_BUFFER_READ)) {
-        if (bufinfo.len < ROMFS_SIZE_MIN) {
-            mp_raise_OSError(MP_ENODEV);
-        }
-        self->filesystem = bufinfo.buf;
-    } else {
-        self->filesystem = (const uint8_t *)(uintptr_t)mp_obj_get_int_truncated(self->memory);
+    mp_get_buffer_raise(self->memory, &bufinfo, MP_BUFFER_READ);
+    if (bufinfo.len < ROMFS_SIZE_MIN) {
+        mp_raise_OSError(MP_ENODEV);
     }
+    self->filesystem = bufinfo.buf;
 
     // Verify it is a ROMFS.
     if (!(self->filesystem[0] == ROMFS_HEADER_BYTE0

tests/extmod/vfs_rom.py

@@ -226,7 +226,8 @@ def test_unknown_record(self):
 class TestStandalone(TestBase):
     def test_constructor(self):
         self.assertIsInstance(vfs.VfsRom(self.romfs), vfs.VfsRom)
-        self.assertIsInstance(vfs.VfsRom(self.romfs_addr), vfs.VfsRom)
+        with self.assertRaises(TypeError):
+            vfs.VfsRom(self.romfs_addr)
 
     def test_mount(self):
         vfs.VfsRom(self.romfs).mount(True, False)