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>

1 files changed, 29 insertions, 0 deletions

diff --git a/tests/micropython/ringio_big.py b/tests/micropython/ringio_big.py
new file mode 100644
index 000000000..d55c4c00b
--- /dev/null
+++ b/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