linux-kernel - Re: [PATCH AUTOSEL 4.19 174/258] livepatch: check kzalloc return values

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Date:   Mon, 28 Jan 2019 18:28:14 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Sasha Levin <sashal@...nel.org>
cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Nicholas Mc Guire <hofrat@...dl.org>,
        Jiri Kosina <jkosina@...e.cz>, live-patching@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 4.19 174/258] livepatch: check kzalloc return
 values

On Mon, 28 Jan 2019, Sasha Levin wrote:

> From: Nicholas Mc Guire <hofrat@...dl.org>
> 
> [ Upstream commit 5f30b2e823484ce6a79f2b59901b6351c15effa6 ]
> 
> 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")
> Acked-by: Joe Lawrence <joe.lawrence@...hat.com>
> Reviewed-by: Petr Mladek <pmladek@...e.com>
> Acked-by: Miroslav Benes <mbenes@...e.cz>
> Signed-off-by: Jiri Kosina <jkosina@...e.cz>
> Signed-off-by: Sasha Levin <sashal@...nel.org>

Hi Sasha,

I am not sure what stable policy is, but the patch is for samples/ 
directory and I do not think it is something which should necessarily go 
to stable. It is your call though.

Regards,
Miroslav

> ---
>  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 49b13553eaae..e8f1bd6b29b1 100644
> --- a/samples/livepatch/livepatch-shadow-fix1.c
> +++ b/samples/livepatch/livepatch-shadow-fix1.c
> @@ -89,6 +89,11 @@ 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 4c54b250332d..4aa8a88d3cd6 100644
> --- a/samples/livepatch/livepatch-shadow-mod.c
> +++ b/samples/livepatch/livepatch-shadow-mod.c
> @@ -118,6 +118,10 @@ 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);
> -- 
> 2.19.1
>