linux-kernel - Re: [PATCH] drm/i915: Prefer struct

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Date:   Wed, 13 Oct 2021 14:24:05 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Len Baker <len.baker@....com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Len Baker <len.baker@....com>, Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/i915: Prefer struct_size over open coded arithmetic

On Mon, 11 Oct 2021, Len Baker <len.baker@....com> wrote:
> Hi,
>
> On Sun, Oct 03, 2021 at 12:42:58PM +0200, Len Baker wrote:
>> As noted in the "Deprecated Interfaces, Language Features, Attributes,
>> and Conventions" documentation [1], size calculations (especially
>> multiplication) should not be performed in memory allocator (or similar)
>> function arguments due to the risk of them overflowing. This could lead
>> to values wrapping around and a smaller allocation being made than the
>> caller was expecting. Using those allocations could lead to linear
>> overflows of heap memory and other misbehaviors.
>>
>> In this case these are not actually dynamic sizes: all the operands
>> involved in the calculation are constant values. However it is better to
>> refactor them anyway, just to keep the open-coded math idiom out of
>> code.
>>
>> So, add at the end of the struct i915_syncmap a union with two flexible
>> array members (these arrays share the same memory layout). This is
>> possible using the new DECLARE_FLEX_ARRAY macro. And then, use the
>> struct_size() helper to do the arithmetic instead of the argument
>> "size + count * size" in the kmalloc and kzalloc() functions.
>>
>> Also, take the opportunity to refactor the __sync_seqno and __sync_child
>> making them more readable.
>>
>> This code was detected with the help of Coccinelle and audited and fixed
>> manually.
>>
>> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments
>>
>> Signed-off-by: Len Baker <len.baker@....com>
>> ---
>>  drivers/gpu/drm/i915/i915_syncmap.c | 12 ++++++++----
>>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> I received a mail telling that this patch doesn't build:
>
> == Series Details ==
>
> Series: drm/i915: Prefer struct_size over open coded arithmetic
> URL   : https://patchwork.freedesktop.org/series/95408/
> State : failure
>
> But it builds without error against linux-next (tag next-20211001). Against
> which tree and branch do I need to build?

drm-tip [1]. It's a sort of linux-next for graphics. I think there are
still some branches that don't feed to linux-next.

BR,
Jani.


[1] https://cgit.freedesktop.org/drm/drm-tip


>
> Regards,
> Len

-- 
Jani Nikula, Intel Open Source Graphics Center