linux-kernel - Re: [PATCH 2/2] livepatch: check kzalloc return values

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Message-ID: <cc9d25f4-fc3b-f399-654b-9de09689acc5@redhat.com>
Date:   Fri, 14 Dec 2018 16:39:39 -0500
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Nicholas Mc Guire <hofrat@...dl.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Jessica Yu <jeyu@...nel.org>, Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] livepatch: check kzalloc return values

On 12/14/2018 11:56 AM, 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 in
> livepatch_fix1_dummy_alloc() respectively dummy_alloc() previous
> allocation is freed (thanks to Petr Mladek <pmladek@...e.com> for
> catching this) and NULL returned.
> 
> Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
> Fixes: 439e7271dc2b ("livepatch: introduce shadow variable API")
> ---
> 
> Problem 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
> 
> Patch is against 4.20-rc6 (localversion-next is next-20181214)
> on top of 0001-livepatch-fix-non-static-warnings.patch 
> 
>  samples/livepatch/livepatch-shadow-fix1.c | 5 +++++
>  samples/livepatch/livepatch-shadow-mod.c  | 4 ++++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
> index eaab10f..1974eb5 100644
> --- a/samples/livepatch/livepatch-shadow-fix1.c
> +++ b/samples/livepatch/livepatch-shadow-fix1.c
> @@ -89,6 +89,11 @@ static __noclone struct dummy *livepatch_fix1_dummy_alloc(void)
>  	 * pointer to handle resource release.
>  	 */
>  	leak = kzalloc(sizeof(int), GFP_KERNEL);
> +	if (!leak) {
> +		kfree(d);
> +		return NULL;
> +	}
> +
>  	klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
>  			 shadow_leak_ctor, leak);
>  
> diff --git a/samples/livepatch/livepatch-shadow-mod.c b/samples/livepatch/livepatch-shadow-mod.c
> index dc69da0..b4ece36 100644
> --- a/samples/livepatch/livepatch-shadow-mod.c
> +++ b/samples/livepatch/livepatch-shadow-mod.c
> @@ -123,6 +123,10 @@ static __noclone noinline struct dummy *dummy_alloc(void)
>  
>  	/* Oops, forgot to save leak! */
>  	leak = kzalloc(sizeof(int), GFP_KERNEL);
> +	if (!leak) {
> +		kfree(d);
> +		return NULL;
> +	}
>  
>  	pr_info("%s: dummy @ %p, expires @ %lx\n",
>  		__func__, d, d->jiffies_expire);
> 

Patch v2 2/2 looks good, thanks for combining.

Acked-by: Joe Lawrence <joe.lawrence@...hat.com>

-- Joe