linux-kernel - Re: [PATCH] drivers/char/ipmi_si: prevent null deref during module exit

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Date:   Wed, 8 Nov 2017 11:11:10 -0600
From:   Andrew Banman <abanman@....com>
To:     Corey Minyard <minyard@....org>
CC:     Dimitri Sivanich <sivanich@....com>,
        "Anderson, Russ" <russ.anderson@....com>,
        Mike Travis <mike.travis@....com>,
        <openipmi-developer@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers/char/ipmi_si: prevent null deref during module
 exit

On 11/8/17 11:06 AM, Andrew Banman wrote:
> If there are uninitialized SMIs in the smi_infos list, i.e. with no
> handlers set, then disable_si_irq() in cleanup_smi_one() will hit a null
> pointer dereference when the former attempts to start the check enables
> transaction. Thus, we panic during module exit.

I think this points to a broader problem of holding uninitialized smi_info
structs in smi_infos list. There are many places where handlers and other struct
members are assumed. Maybe a better design would be to remove SMIs from the list
if we have no intention of initializing them?

Andrew

> 
> Avoid panicking when there are uninitialized SMIs by checking for a handler
> pointer before starting the check enables transaction.
> 
> Signed-off-by: Andrew Banman <abanman@....com>
> ---
>   drivers/char/ipmi/ipmi_si_intf.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/char/ipmi/ipmi_si_intf.c b/drivers/char/ipmi/ipmi_si_intf.c
> index cb5719e..6c0b1b3 100644
> --- a/drivers/char/ipmi/ipmi_si_intf.c
> +++ b/drivers/char/ipmi/ipmi_si_intf.c
> @@ -442,7 +442,7 @@ static void start_check_enables(struct smi_info *smi_info, 
> bool start_timer)
> 
>       if (start_timer)
>           start_new_msg(smi_info, msg, 2);
> -    else
> +    else if (smi_info->handlers)
>           smi_info->handlers->start_transaction(smi_info->si_sm, msg, 2);
>       smi_info->si_state = SI_CHECKING_ENABLES;
>   }