[PATCH] drm/i915: Prefer struct_size over open coded arithmetic

[Len Baker]

Hi Daniel and Jani,

On Wed, Oct 13, 2021 at 01:51:30PM +0200, Daniel Vetter wrote:
> On Wed, Oct 13, 2021 at 02:24:05PM +0300, Jani Nikula wrote:
> > On Mon, 11 Oct 2021, Len Baker <len.baker at gmx.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 at gmx.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.
>
> Yeah we need to get gt-next in linux-next asap. Joonas promised to send
> out his patch to make that happen in dim.
> -Daniel

Is there a possibility that you give an "Acked-by" tag? And then this patch
goes to the mainline through the Kees' tree or Gustavo's tree?

Or is it better to wait for drm-tip to update?

Regards,
Len

>
> >
> > BR,
> > Jani.
> >
> >
> > [1] https://cgit.freedesktop.org/drm/drm-tip
> >
> >
> > >
> > > Regards,
> > > Len
> >
> > --
> > Jani Nikula, Intel Open Source Graphics Center
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch