linux-kernel - Re: [PATCH-next] sched: Fix Null pointer derefrence

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Message-ID: <20210516130129.GA32445@ard0534>
Date:   Sun, 16 May 2021 14:01:29 +0100
From:   Khaled Romdhani <khaledromdhani216@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH-next] sched: Fix Null pointer derefrence

On Sat, May 15, 2021 at 11:02:38PM +0200, Peter Zijlstra wrote:
> On Sat, May 15, 2021 at 05:46:45PM +0100, Khaled ROMDHANI wrote:
> > The 'curr' variable could be NULL and derefrenced by
> > pick_next_entity. Fix this by adding a check that prevent
> > the invocation of pick_next_entity with a NULL passed argument.
> 
> And why exactly is that a problem?
>
Within pick_next_entity, we could have 'left = curr'. 
Thus the function wakeup_preempt_entity which is invoked 
from pick_next_entity, derefrence the the sched entity 'left' 
that may be a NULL passed argument.