Re: [RFC PATCH v3] RDMA/siw: use kzalloc_flex

[Kees Cook <kees@kernel.org>]

On Wed, May 13, 2026 at 11:28:46AM -0300, Jason Gunthorpe wrote:
> Ignore this, kxalloc_flex should not be assumed to initialize anything
> but 0. IDK why they put in the auto-initialize when it cannot be
> relied on, security in depth I guess.

Correct, manual initialization is still always required. The auto-init
(when counted_by is supported) is to deal with adding counted_by to code
that doesn't initialize the counter before access. i.e. this code used
to work:

thing = kzalloc(sizeof(*thing) + n * sizeof(*thing->fam));
access(thing->fam);
thing->fam_count = n;

but if we add counted_by and use kzalloc_flex, suddenly it breaks (at
access() time) unless kzalloc_flex also performs the "fam_count = n"
at alloc time.

-- 
Kees Cook