linux-kernel - Re: [PATCH v2] lkdtm/bugs: Check for the NULL pointer after calling kmalloc

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Message-ID: <20220120035542.GC1978@kadam>
Date:   Thu, 20 Jan 2022 06:55:43 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Jiasheng Jiang <jiasheng@...as.ac.cn>, arnd@...db.de,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] lkdtm/bugs: Check for the NULL pointer after calling
 kmalloc

On Wed, Jan 19, 2022 at 10:45:33AM -0800, Kees Cook wrote:
> > diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
> > index f4cb94a9aa9c..c35ea54824ac 100644
> > --- a/drivers/misc/lkdtm/bugs.c
> > +++ b/drivers/misc/lkdtm/bugs.c
> > @@ -325,6 +325,11 @@ void lkdtm_ARRAY_BOUNDS(void)
> >  
> >  	not_checked = kmalloc(sizeof(*not_checked) * 2, GFP_KERNEL);
> >  	checked = kmalloc(sizeof(*checked) * 2, GFP_KERNEL);
> > +	if (!not_checked || !checked) {
> > +		kfree(not_checked);
> > +		kfree(checked);
> > +		return;
> > +	}
> 
> This should explicitly yell about the memory failure. See the other
> error cases for examples. I'd expect something like this before the
> return:
> 
> 		pr_err("FAIL: could not allocate required buffers\n");

Adding error messages for kmalloc failures is a checkpatch violation.

Those allocations will never fail.  There is already a warning message
and stack trace built into kmalloc().  It's just a waste of resources to
add the warning message.

regards,
dan carpenter