linux-kernel - Re: [PATCH] kernel/exit.c: pointer sighand could be uninitialized

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Date:   Wed, 2 May 2018 23:44:20 -0700
From:   Chengyu Song <csong@...ucr.edu>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Yizhuo Zhai <yzhai003@....edu>, mingo@...nel.org,
        keescook@...omium.org, akpm@...ux-foundation.org,
        paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        Zhiyun Qian <zhiyunq@...ucr.edu>
Subject: Re: [PATCH] kernel/exit.c: pointer sighand could be uninitialized

Right. Should have checked the commit history ... this has been brought up before:

> Peter Zijlstra - May 18, 2016, 5:02 p.m.
> 
> > +struct task_struct *task_rcu_dereference(struct task_struct **ptask)
> > +{
> > +	struct task_struct *task;
> > +	struct sighand_struct *sighand;
> 
> I think that needs: ' = NULL',

and led to the comments added there.

Sorry for wasting your time.

-chengyu

> On May 2, 2018, at 10:06 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> 
> On Wed, May 02, 2018 at 06:48:57PM -0700, Yizhuo Zhai wrote:
>> Variable 'sighand' could be uninitialized if probe_kernel_address fails
>> (-EFAULT). The later use in the if statement may lead to undefined behavior.
> 
> Excuse me, but that's nonsense.  The value *copied* into it (in case
> probe_kernel_address() has not failed) may be just as uninitialized.
> If mere "compare uninitialized pointer value to NULL" can cause nasal demons to fly,
> 	* we are screwed anyway
> 	* the piece of crap compiler should be printed on sandpaper and used to
> polish its authors.
> 
> Read the comments in there, please.  Especially the one regarding the second case.