linux-kernel - Re: [PATCH] soundwire: sysfs_emit() expects a buffer of size PAGE

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Message-ID: <87o6takqd3.wl-tiwai@suse.de>
Date: Thu, 24 Jul 2025 09:19:36 +0200
From: Takashi Iwai <tiwai@...e.de>
To: Sergio Perez Gonzalez <sperezglz@...il.com>
Cc: vkoul@...nel.org,
	yung-chuan.liao@...ux.intel.com,
	pierre-louis.bossart@...ux.dev,
	linux-sound@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] soundwire: sysfs_emit() expects a buffer of size PAGE_SIZE

On Thu, 24 Jul 2025 01:09:25 +0200,
Sergio Perez Gonzalez wrote:
> 
> In read_buffer_show(), allocate sufficient memory to pass on to
> sysfs_emit(), which expects a buffer of size PAGE_SIZE.
> 
> Link: https://scan7.scan.coverity.com/#/project-view/53936/11354?selectedIssue=1648019
> Fixes: 35323d8ab811 ("soundwire: replace scnprintf() with sysfs_emit() for sysfs consistency")
> Signed-off-by: Sergio Perez Gonzalez <sperezglz@...il.com>
> ---
>  drivers/soundwire/debugfs.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/soundwire/debugfs.c b/drivers/soundwire/debugfs.c
> index 825f7abbad32..08fb1e29026e 100644
> --- a/drivers/soundwire/debugfs.c
> +++ b/drivers/soundwire/debugfs.c
> @@ -306,12 +306,12 @@ static int cmd_go(void *data, u64 value)
>  DEFINE_DEBUGFS_ATTRIBUTE(cmd_go_fops, NULL,
>  			 cmd_go, "%llu\n");
>  
> -#define MAX_LINE_LEN 128
> -
>  static int read_buffer_show(struct seq_file *s_file, void *data)
>  {
> -	char buf[MAX_LINE_LEN];
>  	int i;
> +	char *buf __free(kfree) = kzalloc(PAGE_SIZE, GFP_KERNEL);
> +	if (!buf)
> +		return -ENOMEM;

IMO, it's better to scratch the whole previous change.
It makes little sense to allocate a large buffer here just for the
temporary formatting.

Moreover, *_show() functions there take seq_file pointer, and you can
just use seq_printf() directly.  The sysfs/kobject show callback is
with the a fixed PAGE_SIZE buffer, hence sysfs_emit() is useful, but
in this case, it's a completely different story.


thanks,

Takashi