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Tue, 15 Dec 2020 14:30:53 +0000 Subject: Re: [patch 012/200] mm: slab: clarify krealloc()'s behavior with __GFP_ZERO To: Andrew Morton , airlied@linux.ie, alexander.shishkin@linux.intel.com, andriy.shevchenko@linux.intel.com, bgolaszewski@baylibre.com, bp@alien8.de, bp@suse.de, cl@linux.com, daniel.vetter@ffwll.ch, daniel@ffwll.ch, gustavo@padovan.org, iamjoonsoo.kim@lge.com, james.morse@arm.com, jasowang@redhat.com, linus.walleij@linaro.org, linux-mm@kvack.org, maarten.lankhorst@linux.intel.com, mchehab@kernel.org, mm-commits@vger.kernel.org, mripard@kernel.org, mst@redhat.com, penberg@kernel.org, perex@perex.cz, rientjes@google.com, rric@kernel.org, sumit.semwal@linaro.org, tiwai@suse.com, tiwai@suse.de, tony.luck@intel.com, torvalds@linux-foundation.org, tzimmermann@suse.de, vbabka@suse.cz References: <20201215030350.xC0HoDUgG%akpm@linux-foundation.org> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: <2172e342-e73f-a759-fce5-8b94daafd506@amd.com> Date: Tue, 15 Dec 2020 15:30:44 +0100 User-Agent: Mozilla/5.0 (X11; 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This is why we have helpers like kmalloc_array(). > > However we don't have krealloc_array() equivalent and there are many users > who do their own multiplication when calling krealloc() for arrays. > > This series provides krealloc_array() and uses it in a couple places. > > A separate series will follow adding devm_krealloc_array() which is needed > in the xilinx adc driver. > > > This patch (of 9): > > __GFP_ZERO is ignored by krealloc() (unless we fall-back to kmalloc() > path, in which case it's honored). Point that out in the kerneldoc. > > Link: https://lkml.kernel.org/r/20201109110654.12547-1-brgl@bgdev.pl > Link: https://lkml.kernel.org/r/20201109110654.12547-2-brgl@bgdev.pl > Signed-off-by: Bartosz Golaszewski > Cc: Andy Shevchenko > Cc: Sumit Semwal > Cc: Gustavo Padovan > Cc: Christian Knig > Cc: Mauro Carvalho Chehab > Cc: Borislav Petkov > Cc: Tony Luck > Cc: James Morse > Cc: Robert Richter > Cc: Maarten Lankhorst > Cc: Maxime Ripard > Cc: Thomas Zimmermann > Cc: David Airlie > Cc: Daniel Vetter > Cc: Alexander Shishkin > Cc: Linus Walleij > Cc: "Michael S . Tsirkin" > Cc: Jason Wang > Cc: Christoph Lameter > Cc: Pekka Enberg > Cc: David Rientjes > Cc: Joonsoo Kim > Cc: Jaroslav Kysela > Cc: Takashi Iwai > Cc: Borislav Petkov > Cc: Daniel Vetter > Cc: Takashi Iwai > Cc: Vlastimil Babka > Signed-off-by: Andrew Morton > --- > > mm/slab_common.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > --- a/mm/slab_common.c~mm-slab-clarify-kreallocs-behavior-with-__gfp_zero > +++ a/mm/slab_common.c > @@ -1091,9 +1091,9 @@ static __always_inline void *__do_kreall > * @flags: the type of memory to allocate. > * > * The contents of the object pointed to are preserved up to the > - * lesser of the new and old sizes. If @p is %NULL, krealloc() > - * behaves exactly like kmalloc(). If @new_size is 0 and @p is not a > - * %NULL pointer, the object pointed to is freed. > + * lesser of the new and old sizes (__GFP_ZERO flag is effectively ignored). > + * If @p is %NULL, krealloc() behaves exactly like kmalloc(). If @new_size > + * is 0 and @p is not a %NULL pointer, the object pointed to is freed. Question: Can the fact that __GFP_ZERO is effectively ignored cause an information leak if new size is larger than old size and the array is somehow copied to user space? I think the answer is no, but just wanted to double check. Maybe we should note that here. Thanks, Christian. > * > * Return: pointer to the allocated memory or %NULL in case of error > */ > _