linux-kernel - Re: [PATCH v5 4/4] printk: Give error on attempt to set log buffer length to over 4G

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Message-ID: <20181009135758.GA1419@tigerII.localdomain>
Date:   Tue, 9 Oct 2018 22:57:58 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        zhe.he@...driver.com, rostedt@...dmis.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/4] printk: Give error on attempt to set log buffer
 length to over 4G

On (10/09/18 15:05), Petr Mladek wrote:
> > 
> > Yeah, I think we gonna have problems even with a 4G logbuf and a 32-bit
> > user-space doing syslog(int len).
> > 
> > I agree on the "not motivated enough" part ;)
> 
> OK, I have pushed an updated patch that has the limit 2GB
> into printk.git, for-4.20 branch.
> 
> Note that it is slightly different than the yesterday's proposal.
> I made a mistake in testing and still compared with UNIT_MAX.
> 
> The pushed version can be seen at
> https://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk.git/commit/?h=for-4.20&id=e6fe3e5b7d16e8f146a4ae7fe481bc6e97acde1e


---

> +#define LOG_BUF_LEN_MAX (u32)(1 << 31)
[..]
> +	if (size > (u64)LOG_BUF_LEN_MAX) {
> +		size = (u64)LOG_BUF_LEN_MAX;
> +		pr_err("log_buf over 2G is not supported.\n");
> +	}

Why not INT_MAX?


> +	pr_info("log_buf_len: %u bytes\n", log_buf_len);
> +	pr_info("early log buf free: %u(%u%%)\n",
>  		free, (free * 100) / __LOG_BUF_LEN);

Can 'free * 100' overflow?

	-ss