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From: Hao Li To: "Vlastimil Babka (SUSE)" Cc: Harry Yoo , Christoph Lameter , David Rientjes , Roman Gushchin , Suren Baghdasaryan , Alexei Starovoitov , Andrew Morton , Johannes Weiner , Michal Hocko , Shakeel Butt , Alexander Potapenko , Marco Elver , Dmitry Vyukov , 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 Message-ID: References: <20260610-slab_alloc_flags-v2-0-7190909db118@kernel.org> <20260610-slab_alloc_flags-v2-1-7190909db118@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260610-slab_alloc_flags-v2-1-7190909db118@kernel.org> X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: EC1B4120007 X-Stat-Signature: rayzi93y83oac6szxyzg7wcxrkmx8mzd X-Rspam-User: X-HE-Tag: 1781236046-281498 X-HE-Meta: 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 68Xv/uo8 GThPU2//RSPH7R0lkbEafLyOgiSN0hk0y9fJYD4+IecgagIpONTk8luMy9P9xVauQv9e06LtGC3Aix0b2AMiidhi+ABMQiySrVrjAPh3rnEWeILPSCv5Po5QKljqANVhj8sD4FcyJ0DHUQep7DK1a3iTwHg0VwdeTJeixwdkyIMf8LpebcnYLNYLgdqbNOPqNQJlv/fdn8YYkTmX6kY4cKGxQCtlcpSmE/HSPkM3+mgdHSxWnhxa73YyjTBR5JMa9aBZOrC7qnnjNk1XtWlDQUsddEr8VI1YOToldo5+CU/AMLrZJKlBwxwJlHg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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: > Signed-off-by: Vlastimil Babka (SUSE) > --- Reviewed-by: Hao Li -- Thanks, Hao