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

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Date:   Mon, 11 Oct 2021 11:23:04 +0200
From:   Len Baker <len.baker@....com>
To:     Jani Nikula <jani.nikula@...ux.intel.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

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?

Regards,
Len