linux-kernel - Re: [PATCH v2 0/5] mm/slub: Improve data handling of krealloc() when orig

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Message-ID: <202410141338.EA1D30F3@keescook>
Date: Mon, 14 Oct 2024 13:40:01 -0700
From: Kees Cook <kees@...nel.org>
To: Feng Tang <feng.tang@...el.com>
Cc: Vlastimil Babka <vbabka@...e.cz>, Marco Elver <elver@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Hyeonggon Yoo <42.hyeyoo@...il.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Shuah Khan <skhan@...uxfoundation.org>,
	David Gow <davidgow@...gle.com>, Danilo Krummrich <dakr@...nel.org>,
	Alexander Potapenko <glider@...gle.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Vincenzo Frascino <vincenzo.frascino@....com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH v2 0/5] mm/slub: Improve data handling of krealloc() when
 orig_size is enabled

On Mon, Oct 14, 2024 at 10:20:36PM +0800, Feng Tang wrote:
> On Mon, Oct 14, 2024 at 03:12:09PM +0200, Vlastimil Babka wrote:
> > On 10/14/24 14:52, Feng Tang wrote:
> > > On Mon, Oct 14, 2024 at 10:53:32AM +0200, Vlastimil Babka wrote:
> > >> On 10/14/24 09:52, Feng Tang wrote:
> > > OK, originally I tried not to expose internals of __ksize(). Let me
> > > try this way.
> > 
> > ksize() makes assumptions that a user outside of slab itself is calling it.
> > 
> > But we (well mostly Kees) also introduced kmalloc_size_roundup() to avoid
> > querying ksize() for the purposes of writing beyond the original
> > kmalloc(size) up to the bucket size. So maybe we can also investigate if the
> > skip_orig_size_check() mechanism can be removed now?
> 
> I did a quick grep, and fortunately it seems that the ksize() user are
> much less than before. We used to see some trouble in network code, which
> is now very clean without the need to skip orig_size check. Will check
> other call site later.

Right -- only things that are performing a reallocation should be using
ksize(). e.g. see __slab_build_skb()

-- 
Kees Cook