linux-kernel - Re: [PATCH] drm/i915/gvt: don't dereference 'workload' before null checking it

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Date:   Wed, 21 Mar 2018 19:23:24 +0000
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     Colin Ian King <colin.king@...onical.com>,
        "Joe Perches" <joe@...ches.com>,
        "Zhenyu Wang" <zhenyuw@...ux.intel.com>,
        "Zhi Wang" <zhi.a.wang@...el.com>,
        "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>,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/i915/gvt: don't dereference 'workload' before null checking
 it

Quoting Colin Ian King (2018-03-21 19:18:28)
> On 21/03/18 19:09, Joe Perches wrote:
> > On Wed, 2018-03-21 at 19:06 +0000, Colin King wrote:
> >> From: Colin Ian King <colin.king@...onical.com>
> >>
> >> The pointer workload is dereferenced before it is null checked, hence
> >> there is a potential for a null pointer dereference on workload. Fix
> >> this by only dereferencing workload after it is null checked.
> >>
> >> Detected by CoverityScan, CID#1466017 ("Dereference before null check")
> > 
> > Maybe true, but is it possible for workload to be null?
> > Maybe the null test should be removed instead.
> 
> From what I understand from the static analysis, there may be a
> potential for workload to be null, I couldn't rule it out so I went with
> the more paranoid stance of keeping the null check in.

Not sr_oa_regs() problem if workload is NULL, that's the callers. I
reviewed the identical patch yesterday, and we ended up with removing
the NULL checks, just keeping the workload->id != RCS.
-Chris