extmod/vfs_blockdev: Check block device function positive results.

projectgus · projectgus · commit a26ccdd4e653 · 2024-01-31T18:19:39.000+11:00
A positive result here can result in eventual memory corruption as littlefs expects the result of a cache read/write function to be 0 or a negative integer for an error. Closes micropython#13046 This work was funded through GitHub Sponsors. Signed-off-by: Angus Gratton <angus@redyak.com.au>
diff --git a/extmod/vfs_blockdev.c b/extmod/vfs_blockdev.c
@@ -32,6 +32,18 @@
 
 #if MICROPY_VFS
 
+// Block device functions are expected to return 0 on success
+// and negative integer on errors. Check for positive integer
+// results as some callers (i.e. littlefs) will produce corrupt
+// results from these.
+STATIC int mp_vfs_check_result(mp_obj_t ret) {
+    int i = MP_OBJ_SMALL_INT_VALUE(ret);
+    if (i > 0) {
+        mp_raise_OSError(MP_EINVAL);
+    }
+    return i;
+}
+
 void mp_vfs_blockdev_init(mp_vfs_blockdev_t *self, mp_obj_t bdev) {
     mp_load_method(bdev, MP_QSTR_readblocks, self->readblocks);
     mp_load_method_maybe(bdev, MP_QSTR_writeblocks, self->writeblocks);
@@ -69,7 +81,7 @@ int mp_vfs_blockdev_read_ext(mp_vfs_blockdev_t *self, size_t block_num, size_t b
     if (ret == mp_const_none) {
         return 0;
     } else {
-        return MP_OBJ_SMALL_INT_VALUE(ret);
+        return mp_vfs_check_result(ret);
     }
 }
 
@@ -106,7 +118,7 @@ int mp_vfs_blockdev_write_ext(mp_vfs_blockdev_t *self, size_t block_num, size_t
     if (ret == mp_const_none) {
         return 0;
     } else {
-        return MP_OBJ_SMALL_INT_VALUE(ret);
+        return mp_vfs_check_result(ret);
     }
 }
 
