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

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

[Junrui Luo]

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>
---
 sound/firewire/motu/motu-hwdep.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/sound/firewire/motu/motu-hwdep.c b/sound/firewire/motu/motu-hwdep.c
index 981c19430cb0..6675b23aad69 100644
--- 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);
 

---
base-commit: 4a26e7032d7d57c998598c08a034872d6f0d3945
change-id: 20251203-fixes-40c38e3ecb04

Best regards,
-- 
Junrui Luo <moonafterrain@outlook.com>

Re: [PATCH] ALSA: firewire-motu: fix buffer overflow in hwdep read for DSP events

[Takashi Iwai]

On Wed, 03 Dec 2025 05:27:03 +0100,
Junrui Luo wrote:
> 
> 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>

Applied now.  Thanks.

BTW, the code there has another bug; the loop of put_user() above your
change doesn't check whether it has an enough remaining size.  When
count isn't aligned with 4 bytes, it might cause a similar overwrite.
It has to be corrected, too.


Takashi