linux-kernel - Re: [PATCH 1/3] ALSA: timer: fix NULL pointer dereference in read()/ioctl() race

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Message-ID: <0560accf-2461-8205-6377-32b464bfce7e@oracle.com>
Date:   Mon, 29 Aug 2016 09:14:15 +0200
From:   Vegard Nossum <vegard.nossum@...cle.com>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Jaroslav Kysela <perex@...ex.cz>, alsa-devel@...a-project.org,
        syzkaller <syzkaller@...glegroups.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] ALSA: timer: fix NULL pointer dereference in
 read()/ioctl() race

On 08/29/2016 09:02 AM, Takashi Iwai wrote:
> On Mon, 29 Aug 2016 00:33:49 +0200,
> Vegard Nossum wrote:
>> @@ -1602,15 +1602,25 @@ static int snd_timer_user_tselect(struct file *file,
>>  	kfree(tu->tqueue);
>>  	tu->tqueue = NULL;
>>  	if (tu->tread) {
>> -		tu->tqueue = kmalloc(tu->queue_size * sizeof(struct snd_timer_tread),
>> +		struct snd_timer_tread *ttr;
>> +		ttr = kmalloc(tu->queue_size * sizeof(struct snd_timer_tread),
>>  				     GFP_KERNEL);
>> -		if (tu->tqueue == NULL)
>> +		if (ttr) {
>> +			kfree(tu->tqueue);
>> +			tu->tqueue = ttr;
>
> This looks like the double-tree, as you didn't remove the kfree() call
> in the above.  But, I guess this change is superfluous when you
> introduce the mutex at...

You're right, this hunk is garbage.

Please see the new patch (attached), I also changed the patch
description slightly to match the changes.

I'll start running some tests on the new patch.

Thanks!


Vegard

View attachment "0001-ALSA-timer-fix-NULL-pointer-dereference-in-read-ioct.patch" of type "text/x-patch" (4171 bytes)