py/objringio: Detect incorrect constructor calls.

ringbuffer.size must be at least 2, and is a 16-bit quantity.

This fixes several cases including the one the fuzzer discovered, which
would lead to a fatal signal when accessing the object.

Fixes issue #17847.

Signed-off-by: Jeff Epler <jepler@gmail.com>

py/objringio.c

@@ -39,22 +39,19 @@ typedef struct _micropython_ringio_obj_t {
 
 static mp_obj_t micropython_ringio_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args) {
     mp_arg_check_num(n_args, n_kw, 1, 1, false);
-    mp_int_t buff_size = -1;
     mp_buffer_info_t bufinfo = {NULL, 0, 0};
 
     if (!mp_get_buffer(args[0], &bufinfo, MP_BUFFER_RW)) {
-        buff_size = mp_obj_get_int(args[0]);
+        bufinfo.len = mp_obj_get_int(args[0]) + 1;
+        bufinfo.buf = m_new(uint8_t, bufinfo.len);
+    }
+    if (bufinfo.len < 2 || bufinfo.len > UINT16_MAX) {
+        mp_raise_ValueError(NULL);
     }
     micropython_ringio_obj_t *self = mp_obj_malloc(micropython_ringio_obj_t, type);
-    if (bufinfo.buf != NULL) {
-        // buffer passed in, use it directly for ringbuffer.
-        self->ringbuffer.buf = bufinfo.buf;
-        self->ringbuffer.size = bufinfo.len;
-        self->ringbuffer.iget = self->ringbuffer.iput = 0;
-    } else {
-        // Allocate new buffer, add one extra to buff_size as ringbuf consumes one byte for tracking.
-        ringbuf_alloc(&(self->ringbuffer), buff_size + 1);
-    }
+    self->ringbuffer.buf = bufinfo.buf;
+    self->ringbuffer.size = bufinfo.len;
+    self->ringbuffer.iget = self->ringbuffer.iput = 0;
     return MP_OBJ_FROM_PTR(self);
 }
 

tests/micropython/ringio.py

@@ -46,3 +46,21 @@ try:
     micropython.RingIO(None)
 except TypeError as ex:
     print(type(ex))
+
+try:
+    # Buffer may not be empty
+    micropython.RingIO(bytearray(0))
+except ValueError as ex:
+    print(type(ex))
+
+try:
+    # Buffer may not be too small
+    micropython.RingIO(bytearray(1))
+except ValueError as ex:
+    print(type(ex))
+
+try:
+    # Size may not be too small
+    micropython.RingIO(0)
+except ValueError as ex:
+    print(type(ex))

tests/micropython/ringio.py.exp

@@ -14,3 +14,6 @@ b'\x00\x01\x00\x01\x00\x01\x00\x01\x00\x01\x00\x01\x00\x01\x00\x01'
 0
 b'\x00\x01\x00\x01\x00\x01\x00\x01\x00\x01\x00\x01\x00\x01\x00\x01'
 <class 'TypeError'>
+<class 'ValueError'>
+<class 'ValueError'>
+<class 'ValueError'>

tests/micropython/ringio_big.py

@@ -0,0 +1,29 @@
+# Check that micropython.RingIO works correctly.
+
+import micropython
+
+try:
+    micropython.RingIO
+except AttributeError:
+    print("SKIP")
+    raise SystemExit
+
+try:
+    # The maximum possible size
+    micropython.RingIO(bytearray(65535))
+    micropython.RingIO(65534)
+
+    try:
+        # Buffer may not be too big
+        micropython.RingIO(bytearray(65536))
+    except ValueError as ex:
+        print(type(ex))
+
+    try:
+        # Size may not be too big
+        micropython.RingIO(65535)
+    except ValueError as ex:
+        print(type(ex))
+except MemoryError:
+    print("SKIP")
+    raise SystemExit

tests/micropython/ringio_big.py.exp

@@ -0,0 +1,2 @@
+<class 'ValueError'>
+<class 'ValueError'>