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

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: 634ec0b2906e ("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>

diff --git a/sound/firewire/motu/motu-hwdep.c b/sound/firewire/motu/motu-hwdep.c
index 981c19430cb0fe86141b14764567545b98501582..6675b23aad69ef91cbc0b5bc5f8b9cd4aefa50a6 100644 (file)
--- a/sound/firewire/motu/motu-hwdep.c
+++ b/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);