linux-kernel - Re: [PATCH] ipmi: fix unsigned long underflow

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Date:   Mon, 7 Aug 2017 16:41:09 +0800
From:   Weilong Chen <chenweilong@...wei.com>
To:     <minyard@....org>
CC:     <openipmi-developer@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, Corey Minyard <cminyard@...sta.com>
Subject: Re: [PATCH] ipmi: fix unsigned long underflow

Hi Minyard,

I test this patch, it works.

Thanks.

On 2017/7/30 10:20, minyard@....org wrote:
> From: Corey Minyard <cminyard@...sta.com>
>
> When I set the timeout to a specific value such as 500ms, the timeout
> event will not happen in time due to the overflow in function
> check_msg_timeout:
> ...
> 	ent->timeout -= timeout_period;
> 	if (ent->timeout > 0)
> 		return;
> ...
>
> The type of timeout_period is long, but ent->timeout is unsigned long.
> This patch makes the type consistent.
>
> Reported-by: Weilong Chen <chenweilong@...wei.com>
> Signed-off-by: Corey Minyard <cminyard@...sta.com>
> ---
> I like to keep things consistent (though I obviously messed up here)
> and keep variables that should be positive unsigned.
>
> But you are right, there is a bug here and some inconsistency.
> This patch changes timeout_period to be unsigned and fixes the
> check.  Can you try this out?
>
>  drivers/char/ipmi/ipmi_msghandler.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
> index 810b138..c82d9fd 100644
> --- a/drivers/char/ipmi/ipmi_msghandler.c
> +++ b/drivers/char/ipmi/ipmi_msghandler.c
> @@ -4030,7 +4030,8 @@ smi_from_recv_msg(ipmi_smi_t intf, struct ipmi_recv_msg *recv_msg,
>  }
>
>  static void check_msg_timeout(ipmi_smi_t intf, struct seq_table *ent,
> -			      struct list_head *timeouts, long timeout_period,
> +			      struct list_head *timeouts,
> +			      unsigned long timeout_period,
>  			      int slot, unsigned long *flags,
>  			      unsigned int *waiting_msgs)
>  {
> @@ -4043,8 +4044,8 @@ static void check_msg_timeout(ipmi_smi_t intf, struct seq_table *ent,
>  	if (!ent->inuse)
>  		return;
>
> -	ent->timeout -= timeout_period;
> -	if (ent->timeout > 0) {
> +	if (timeout_period < ent->timeout) {
> +		ent->timeout -= timeout_period;
>  		(*waiting_msgs)++;
>  		return;
>  	}
> @@ -4110,7 +4111,8 @@ static void check_msg_timeout(ipmi_smi_t intf, struct seq_table *ent,
>  	}
>  }
>
> -static unsigned int ipmi_timeout_handler(ipmi_smi_t intf, long timeout_period)
> +static unsigned int ipmi_timeout_handler(ipmi_smi_t intf,
> +					 unsigned long timeout_period)
>  {
>  	struct list_head     timeouts;
>  	struct ipmi_recv_msg *msg, *msg2;
>