[alsa-devel] [patch v3] ALSA: rawmidi: fix the get next midi device ioctl

[Jaroslav Kysela]

On Thu, 9 Sep 2010, Takashi Iwai wrote:

> At Thu, 9 Sep 2010 00:11:41 +0200,
> Dan Carpenter wrote:
>>
>> If we pass in a device which is higher than SNDRV_RAWMIDI_DEVICES then
>> the "next device" should be -1.  This function just returns device + 1.
>>
>> But the main thing is that "device + 1" can lead to a (harmless) integer
>> overflow and that annoys static analysis tools.
>>
>> Signed-off-by: Dan Carpenter <error27 at gmail.com>
>> ---
>> V2:  In the first version I made negative values return -EINVAL
>> V3:  We shouldn't return -EINVAL for numbers which are too large but
>>      just set the next device to -1.
>>
>> diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c
>> index eb68326..df67605 100644
>> --- a/sound/core/rawmidi.c
>> +++ b/sound/core/rawmidi.c
>> @@ -829,6 +829,8 @@ static int snd_rawmidi_control_ioctl(struct snd_card *card,
>>
>>  		if (get_user(device, (int __user *)argp))
>>  			return -EFAULT;
>> +		if (device > SNDRV_RAWMIDI_DEVICES) /* next device is -1 */
>> +			device = SNDRV_RAWMIDI_DEVICES;
>>  		mutex_lock(&register_mutex);
>>  		device = device < 0 ? 0 : device + 1;
>>  		while (device < SNDRV_RAWMIDI_DEVICES) {
>>
>
> We still need to cover the case device == SNDRV_RAWMIDI_DEVICES.
> Also, device is incremented, so it has to be SNDRV_RAWMIDI_DEVICE - 1.
> i.e.
>
>> +		if (device >= SNDRV_RAWMIDI_DEVICES) /* next device is -1 */
>> +			device = SNDRV_RAWMIDI_DEVICES - 1;
>
>
> I applied the fixed patch now.

Maybe a goto to 'device = -1' line from the condition above might be more 
light (resulted instruction code size) and understandable for this case.

 						Jaroslav

-----
Jaroslav Kysela <perex at perex.cz>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.