From 71044a4186bda22477e7daf98e718c144d22d519 Mon Sep 17 00:00:00 2001 From: Angus Gratton Date: Wed, 20 Mar 2024 16:19:33 +1100 Subject: [PATCH] py/parse: Zero out dangling parse tree pointer to fix potential GC leak. This fixes a bug where a random Python object may become un-garbage-collectable until an enclosing Python file (compiled on device) finishes executing. Details: The mp_parse_tree_t structure is stored on the stack in top-level functions such as parse_compile_execute() in pyexec.c (and others). Although it quickly falls out of scope in these functions, it is usually still in the current stack frame when the compiled code executes. (Compiler dependent, but usually it's one stack push per function.) This means if any Python object happens to allocate at the same address as the (freed) root parse tree chunk, it's un-garbage-collectable as there's a (dangling) pointer up the stack referencing this same address. As reported by @GitHubsSilverBullet here: https://github.com/orgs/micropython/discussions/14116#discussioncomment-8837214 This work was funded through GitHub Sponsors. Signed-off-by: Angus Gratton --- py/parse.c | 1 + 1 file changed, 1 insertion(+) diff --git a/py/parse.c b/py/parse.c index 54be8b97d0..1392303e6f 100644 --- a/py/parse.c +++ b/py/parse.c @@ -1386,6 +1386,7 @@ void mp_parse_tree_clear(mp_parse_tree_t *tree) { m_del(byte, chunk, sizeof(mp_parse_chunk_t) + chunk->alloc); chunk = next; } + tree->chunk = NULL; // Avoid dangling pointer that may live on stack } #endif // MICROPY_ENABLE_COMPILER