linux-kernel - Re: [PATCH] kernel: relay: Improve exception handling in relay_create

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Date: Tue, 2 Jan 2024 11:31:17 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Markus Elfring <Markus.Elfring@....de>
Cc: kernel-janitors@...r.kernel.org, Ahelenia Ziemiańska
 <nabijaczleweli@...ijaczleweli.xyz>, Li kunyu <kunyu@...china.com>, Michal
 Hocko <mhocko@...e.com>, Sebastian Reichel
 <sebastian.reichel@...labora.com>, Suren Baghdasaryan <surenb@...gle.com>,
 Zhang Zhengming <zhang.zhengming@....com>, Zhou Kete <zhou.kete@....com>,
 LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel: relay: Improve exception handling in
 relay_create_buf()

On Sun, 31 Dec 2023 10:38:10 +0100 Markus Elfring <Markus.Elfring@....de> wrote:

> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Sun, 31 Dec 2023 10:26:25 +0100
> 
> The kfree() function was called in one case by
> the relay_create_buf() function during error handling
> even if the passed data structure member contained a null pointer.
> This issue was detected by using the Coccinelle software.
> 
> Thus use another label.
> 
> ...
>
> --- a/kernel/relay.c
> +++ b/kernel/relay.c
> @@ -161,14 +161,15 @@ static struct rchan_buf *relay_create_buf(struct rchan *chan)
> 
>  	buf->start = relay_alloc_buf(buf, &chan->alloc_size);
>  	if (!buf->start)
> -		goto free_buf;
> +		goto free_padding;
> 
>  	buf->chan = chan;
>  	kref_get(&buf->chan->kref);
>  	return buf;
> 
> -free_buf:
> +free_padding:
>  	kfree(buf->padding);
> +free_buf:
>  	kfree(buf);
>  	return NULL;
>  }

kfree(NULL) is an OK thing to do, and is a well-known pattern.  Can we
arrange for Coccinelle to understand this?