From: Hao Li <hao.li@linux.dev>
To: "Vlastimil Babka (SUSE)" <vbabka@kernel.org>
Cc: Harry Yoo <harry@kernel.org>, Christoph Lameter <cl@gentwo.org>,
David Rientjes <rientjes@google.com>,
Roman Gushchin <roman.gushchin@linux.dev>,
Suren Baghdasaryan <surenb@google.com>,
Alexei Starovoitov <ast@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Shakeel Butt <shakeel.butt@linux.dev>,
Alexander Potapenko <glider@google.com>,
Marco Elver <elver@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
kasan-dev@googlegroups.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH v2 01/16] mm/slab: do not limit zeroing to orig_size when only red zoning is enabled
Date: Fri, 12 Jun 2026 11:47:10 +0800 [thread overview]
Message-ID: <aiuArH73S7k_jQ5L@fedora> (raw)
In-Reply-To: <20260610-slab_alloc_flags-v2-1-7190909db118@kernel.org>
On Wed, Jun 10, 2026 at 05:40:03PM +0200, Vlastimil Babka (SUSE) wrote:
> When init (zeroing) on allocation is requested, for kmalloc() we
> generally have to zero the full object size even if a smaller size is
> requested, in order to provide krealloc()'s __GFP_ZERO guarantees.
>
> But if we track the requested size, krealloc() uses that information to
> do the right thing. With red zoning also enabled, any unused size
> became part of the red zone, so it must not be zeroed.
>
> However the check is imprecise, and will trigger also when only
> SLAB_RED_ZONE is enabled without SLAB_STORE_USER. This means enabling
> red zoning alone can compromise krealloc()'s __GFP_ZERO contract.
>
> Fix this by using slub_debug_orig_size() instead, which is the exact
> check for whether the requested size is tracked. We don't need to care
> if red zoning is also enabled or not. Also update and expand the
> comment accordingly.
>
> Fixes: 9ce67395f5a0 ("mm/slub: only zero requested size of buffer for kzalloc when debug enabled")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> ---
Reviewed-by: Hao Li <hao.li@linux.dev>
--
Thanks,
Hao
prev parent reply other threads:[~2026-06-12 3:47 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-10 15:40 [PATCH v2 00/16] mm/slab: introduce alloc_flags and slab_alloc_context Vlastimil Babka (SUSE)
2026-06-10 15:40 ` [PATCH v2 01/16] mm/slab: do not limit zeroing to orig_size when only red zoning is enabled Vlastimil Babka (SUSE)
2026-06-11 4:28 ` Harry Yoo
2026-06-12 3:47 ` Hao Li [this message]
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