Re: [PATCH 1/3] lib/maple_tree: fix potential NULL dereference in mas_pop_node()

Pedro Falcato
2026-03-12T23:22:52Z

On Thu, Mar 12, 2026 at 01:45:31PM -0700, Andrew Morton wrote:
> On Thu, 12 Mar 2026 18:40:53 +0000 Josh Law <hlcj1234567@gmail.com> wrote:
>
> > If kmem_cache_alloc_from_sheaf() returns NULL (possible under
> > GFP_NOWAIT pressure), mas_pop_node() falls through to the out label
> > and dereferences the NULL pointer in memset(ret, 0, sizeof(*ret)).
>
> This is such a glaring bug that I wonder if we're missing something.

According to my local copy of lib/maple_tree.c:

mas_pop_node() - Get a previously allocated maple node from the maple state.

Note the "previously" :) kmem_cache_alloc_from_sheaf() can only fail if you
run out of objects in the sheaf.

So yeah, this "bug" looks bogus.

--
Pedro