linux-kernel - Re: [drm-intel:topic/core-stuff 32/37] drivers/gpu/drm/drm_crtc.c:4472 drm_mode_crtc_set_gamma_size() warn: double check that we're allocating correct size: 2 vs 6

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Message-ID: <CAKMK7uGg7cpKvU=VUgDBmeNYVrj-8yeSv=RBVruMrWkZorhESg@mail.gmail.com>
Date:	Wed, 10 Dec 2014 15:55:02 +0100
From:	Daniel Vetter <daniel.vetter@...ll.ch>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	kbuild@...org, Thierry Reding <treding@...dia.com>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [drm-intel:topic/core-stuff 32/37] drivers/gpu/drm/drm_crtc.c:4472
 drm_mode_crtc_set_gamma_size() warn: double check that we're allocating
 correct size: 2 vs 6

Forgotten to add mailing lists.
-Daniel

On Wed, Dec 10, 2014 at 3:53 PM, Daniel Vetter <daniel.vetter@...ll.ch> wrote:
> On Wed, Dec 10, 2014 at 3:03 PM, Dan Carpenter <dan.carpenter@...cle.com> wrote:
>> From a style prespective this should be:
>>
>>         crtc->gamma_store = kcalloc(gamma_size * 3, sizeof(uint16_t),
>>                                     GFP_KERNEL);
>>
>> Because the elements are sizeof(uint16_t), we are allocating 3
>> arrays of gamma_size elements.  But I guess it's nice to move all the
>> constants to one side of the equation so that it tests for integer
>> overflows...  Whatever you decided is fine, this is a one time email
>> that is auto-genenerated.
>
> Imo the point of kcalloc and kmalloc_array is to get the overflow
> checks correct. Putting the *3 to the gamma_size (which can be fairly
> big and migth come from dubios places) means we still have to deal
> with overflow headaches. sizeof(uint16_t)*3 is trivial to see that
> it's not overflowing.
>
> I think your style guide here is exactly _not_ what we should do as
> best practice for safe code.
> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch



-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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