linux-kernel - Re: [PATCH 1/2] livepatch: handle kzalloc failure

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Date:   Thu, 13 Dec 2018 15:00:58 +0100
From:   Nicholas Mc Guire <der.herr@...r.at>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Nicholas Mc Guire <hofrat@...dl.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jessica Yu <jeyu@...nel.org>, Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] livepatch: handle kzalloc failure

On Thu, Dec 13, 2018 at 01:31:39PM +0100, Petr Mladek wrote:
> On Thu 2018-12-13 12:09:49, Nicholas Mc Guire wrote:
> > kzalloc() return should always be checked - notably in example code
> > where this may be seen as reference. On failure of allocation
> > livepatch_fix1_dummy_alloc() should return NULL.
> > 
> > Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
> > ---
> > 
> > Problem was located with an experimental coccinelle script
> > 
> > Patch was compile tested with: x86_64_defconfig + FTRACE=y
> > FUNCTION_TRACER=y, EXPERT=y, LATENCYTOP=y, SAMPLES=y, SAMPLE_LIVEPATCH=y
> > (with some unrelated sparse warnings on symbols not being static)
> > 
> > Patch is against 4.20-rc6 (localversion-next is next-20181213)
> > 
> >  samples/livepatch/livepatch-shadow-fix1.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
> > index 49b1355..a0e8f04 100644
> > --- a/samples/livepatch/livepatch-shadow-fix1.c
> > +++ b/samples/livepatch/livepatch-shadow-fix1.c
> > @@ -89,6 +89,9 @@ struct dummy *livepatch_fix1_dummy_alloc(void)
> >  	 * pointer to handle resource release.
> >  	 */
> >  	leak = kzalloc(sizeof(int), GFP_KERNEL);
> > +	if (!leak)
> > +		return NULL;
> 
> It should be:
> 
> 	if (!leak) {
> 		kfree(d);
> 		return NULL;
> 	}
> 
> Note that The check is not strictly needed in this artificial
> example because we never read/write any data there. But I agree
> that we should add the check to promote the the right programming
> patterns.
>
thanks for catching this !
will send a V2.

thx!
hofrat