linux-kernel - Re: [PATCH] printk: drop redundant devkmsg_log

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Message-ID: <20180119091707.0a15a24d@gandalf.local.home>
Date:   Fri, 19 Jan 2018 09:17:07 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Petr Mladek <pmladek@...e.com>, linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH] printk: drop redundant devkmsg_log_str memsets

On Fri, 19 Jan 2018 13:39:01 +0900
Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> wrote:

> We copy in null terminated strings "on" and "off", no
> need to zero out devkmsg_log_str in control_devkmsg().
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> ---
>  kernel/printk/printk.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index d70927c384f3..9faddcfd3994 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -136,13 +136,10 @@ static int __init control_devkmsg(char *str)
>  	/*
>  	 * Set sysctl string accordingly:
>  	 */
> -	if (devkmsg_log == DEVKMSG_LOG_MASK_ON) {
> -		memset(devkmsg_log_str, 0, DEVKMSG_STR_MAX_SIZE);
> -		strncpy(devkmsg_log_str, "on", 2);
> -	} else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF) {
> -		memset(devkmsg_log_str, 0, DEVKMSG_STR_MAX_SIZE);
> -		strncpy(devkmsg_log_str, "off", 3);
> -	}
> +	if (devkmsg_log == DEVKMSG_LOG_MASK_ON)
> +		strcpy(devkmsg_log_str, "on");
> +	else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF)
> +		strcpy(devkmsg_log_str, "off");
>  	/* else "ratelimit" which is set by default. */
>  
>  	/*

Yep, and even the sysctl checks for the terminating nul string, so
there's no leaks of any kind.

Tested by adding: printk.devkmsg=on and running:

 $ hexdump -C /proc/sys/kernel/printk_devkmsg
00000000  6f 6e 0a                                          |on.|
00000003


Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve