linux-kernel - Re: [PATCH v2 1/2] printk: Fix panic caused by passing log_buf

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Date:   Tue, 25 Sep 2018 23:31:05 +0800
From:   He Zhe <zhe.he@...driver.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>
CC:     Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] printk: Fix panic caused by passing log_buf_len to
 command line



On 2018年09月25日 21:31, Sergey Senozhatsky wrote:
> On (09/25/18 14:23), Petr Mladek wrote:
>> The 32GB was mentioned as an example one year ego. This is not enough
>> for a new syscall from my point of view.
> I agree. I didn't think of syslog(); was merely thinking about logbuf
> and flushing it to the consoles. syslog() stuff is a bit complex. We
> sort of don't expect user space to allocate 64G to read all log_buf
> messages, do we.
>
> I'm wondering if we can do something like this
>
> ---
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index cf275f4d7912..1b48b61da8fe 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1110,9 +1110,15 @@ static void __init log_buf_len_update(unsigned size)
>  /* save requested log_buf_len since it's too early to process it */
>  static int __init log_buf_len_setup(char *str)
>  {
> -	unsigned size = memparse(str, &str);
> +	u64 size = memparse(str, &str);
>  
> -	log_buf_len_update(size);
> +	if (size > UINT_MAX) {
> +		size = UINT_MAX;
> +		pr_err("log_buf over 4G is not supported. "
> +			"Please contact printk maintainers.\n");
> +	}
> +
> +	log_buf_len_update((unsigned int)size);
>  
>  	return 0;
>  }
>
> ---
>
> So we could know that "the day has come".

I agree on this idea, a good way to collect the potential requirement.
I can send v4 with it if no objection from other people.

Thanks,
Zhe

>
> 	-ss
>