ALSA: firewire-motu: fix buffer overflow in hwdep read for DSP events

[ Upstream commit 210d77c ]

The DSP event handling code in hwdep_read() could write more bytes to
the user buffer than requested, when a user provides a buffer smaller
than the event header size (8 bytes).

Fix by using min_t() to clamp the copy size, This ensures we never copy
more than the user requested.

Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Reported-by: Junrui Luo <moonafterrain@outlook.com>
Fixes: 634ec0b ("ALSA: firewire-motu: notify event for parameter change in register DSP model")
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Link: https://patch.msgid.link/SYBPR01MB78810656377E79E58350D951AFD9A@SYBPR01MB7881.ausprd01.prod.outlook.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: avasummer

sound/firewire/motu/motu-hwdep.c

@@ -83,10 +83,11 @@ static long hwdep_read(struct snd_hwdep *hwdep, char __user *buf, long count,
 		event.motu_register_dsp_change.type = SNDRV_FIREWIRE_EVENT_MOTU_REGISTER_DSP_CHANGE;
 		event.motu_register_dsp_change.count =
 			(consumed - sizeof(event.motu_register_dsp_change)) / 4;
-		if (copy_to_user(buf, &event, sizeof(event.motu_register_dsp_change)))
+		if (copy_to_user(buf, &event,
+				 min_t(long, count, sizeof(event.motu_register_dsp_change))))
 			return -EFAULT;
 
-		count = consumed;
+		count = min_t(long, count, consumed);
 	} else {
 		spin_unlock_irq(&motu->lock);