linux-kernel - Re: [PATCH] tty:vt: Add check the return value of kzalloc to avoid oops

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Date:   Fri, 20 Sep 2019 08:04:26 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Nicolas Pitre <nico@...xnic.net>
Cc:     Xiaoming Ni <nixiaoming@...wei.com>, penberg@...helsinki.fi,
        jslaby@...e.com, textshell@...uujin.de, sam@...nborg.org,
        daniel.vetter@...ll.ch, mpatocka@...hat.com, ghalat@...hat.com,
        linux-kernel@...r.kernel.org, yangyingliang@...wei.com,
        yuehaibing@...wei.com, zengweilin@...wei.com
Subject: Re: [PATCH] tty:vt: Add check the return value of kzalloc to avoid
 oops

On Thu, Sep 19, 2019 at 10:56:15PM -0400, Nicolas Pitre wrote:
> On Thu, 19 Sep 2019, Greg KH wrote:
> 
> > On Thu, Sep 19, 2019 at 05:18:15PM +0800, Xiaoming Ni wrote:
> > > Using kzalloc() to allocate memory in function con_init(), but not
> > > checking the return value, there is a risk of null pointer references
> > > oops.
> > > 
> > > Signed-off-by: Xiaoming Ni <nixiaoming@...wei.com>
> > 
> > We keep having this be "reported" :(
> 
> Something probably needs to be "communicated" about that.

I know, but it's also kind of fun to see what these "automated" checkers
find, sometimes the resulting patches almost work properly :)

This one is really close, I think if the likely/unlikely gets cleaned
up, it is viable.

> > >  		vc_cons[currcons].d = vc = kzalloc(sizeof(struct vc_data), GFP_NOWAIT);
> > > +		if (unlikely(!vc)) {
> > > +			pr_warn("%s:failed to allocate memory for the %u vc\n",
> > > +					__func__, currcons);
> > > +			break;
> > > +		}
> > 
> > At init, this really can not happen.  Have you see it ever happen?
> 
> This is maybe too subtle a fact. The "communication" could be done with 
> some GFP_WONTFAIL flag, and have the allocator simply pannic() if it 
> ever fails.

That's a good idea to do as well.

thanks,

greg k-h