linux-kernel - Re: [PATCH] sysctl: add bound to panic

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Date:   Thu, 9 Jul 2020 20:31:39 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Changming Liu <charley.ashbringer@...il.com>, keescook@...omium.org
Cc:     mcgrof@...nel.org, yzaikin@...gle.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] sysctl: add bound to panic_timeout to prevent overflow

On 7/9/20 8:22 PM, Changming Liu wrote:
> Function panic() in kernel/panic.c will use panic_timeout
> multiplying 1000 as a loop boundery. So this multiplication

                             boundary.

> can overflow when panic_timeout is greater than (INT_MAX/1000).
> And this results in a zero-delay panic, instead of a huge
> timeout as the user intends.
> 
> Fix this by adding bound check to make it no bigger than
> (INT_MAX/1000).
> 
> Signed-off-by: Changming Liu <charley.ashbringer@...il.com>
> ---
>  kernel/sysctl.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index db1ce7a..e60cf04 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -137,6 +137,9 @@ static int minolduid;
>  static int ngroups_max = NGROUPS_MAX;
>  static const int cap_last_cap = CAP_LAST_CAP;
>  
> +/* this is needed for setting boundery for panic_timeout to prevent it from overflow*/

                                 boundary (or max value)                       overflow */

> +static int panic_time_max = INT_MAX / 1000;
> +
>  /*
>   * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
>   * and hung_task_check_interval_secs
> @@ -1857,7 +1860,8 @@ static struct ctl_table kern_table[] = {
>  		.data		= &panic_timeout,
>  		.maxlen		= sizeof(int),
>  		.mode		= 0644,
> -		.proc_handler	= proc_dointvec,
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra2		= &panic_time_max,
>  	},
>  #ifdef CONFIG_COREDUMP
>  	{
> 

thanks.
-- 
~Randy