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

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Date:   Thu, 13 Dec 2018 13:31:39 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Nicholas Mc Guire <hofrat@...dl.org>
Cc:     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 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.

Best Regards,
Petr