linux-kernel - Re: [PATCH] ipmi: ssif: potential NULL dereference in msg_done

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Date:   Sat, 2 Apr 2022 11:52:47 +0800
From:   baihaowen <baihaowen@...zu.com>
To:     <minyard@....org>
CC:     <openipmi-developer@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ipmi: ssif: potential NULL dereference in
 msg_done_handler()

Dear Corey
Thank you for your kindly reply and suggestion. :)

在 4/1/22 8:48 PM, Corey Minyard 写道:
> On Fri, Apr 01, 2022 at 11:27:45AM +0800, Haowen Bai wrote:
>> msg could be null without checking null and return, but still dereference
>> msg->rsp[2] and will lead to a null pointer trigger.
> Actually:
>
>   If you look at the big picture (how the rest of the code works), it's
>   not possible for msg to be NULL in these cases.  However, being
>   defensive here is probably a good idea.
>
>   There are two of these cases, why didn't you fix both of them?
>
>   This still doesn't fix the problem.  There is an "else if" in both
>   cases that also uses msg.
>
> You can't just look at the output of some code analysis tool and make a
> blind decision like this.  You have to look at the big picture.  And you
> have to analyze the code carefully.
>
> The right way to be defensive here is to add:
> 	if (!msg) {
> 		ipmi_ssif_unlock_cond(ssif_info, flags);
> 		break;
> 	}
> in both cases.  And probably add a log, since this means something else
> went wrong.
>
> Anyway, I'll add a patch for defensive measure and give you credit for
> pointing it out.
>
> -corey
>
>> Signed-off-by: Haowen Bai <baihaowen@...zu.com>
>> ---
>>  drivers/char/ipmi/ipmi_ssif.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/char/ipmi/ipmi_ssif.c b/drivers/char/ipmi/ipmi_ssif.c
>> index f199cc1..9383de3 100644
>> --- a/drivers/char/ipmi/ipmi_ssif.c
>> +++ b/drivers/char/ipmi/ipmi_ssif.c
>> @@ -814,7 +814,7 @@ static void msg_done_handler(struct ssif_info *ssif_info, int result,
>>  		break;
>>  
>>  	case SSIF_GETTING_EVENTS:
>> -		if ((result < 0) || (len < 3) || (msg->rsp[2] != 0)) {
>> +		if ((result < 0) || (len < 3) || (msg && (msg->rsp[2] != 0))) {
>>  			/* Error getting event, probably done. */
>>  			msg->done(msg);
>>  
>> -- 
>> 2.7.4
>>

-- 
Haowen Bai