[PATCH] ALSA: bcd2000: Fix a UAF bug on the error path of probing

[PATCH] ALSA: bcd2000: Fix a UAF bug on the error path of probing

[Zheyu Ma]

When the driver fails in snd_card_register() at probe time, it will free
the 'bcd2k->midi_out_urb' before killing it, which may cause a UAF bug.

The following log can reveal it:

[   50.727020] BUG: KASAN: use-after-free in bcd2000_input_complete+0x1f1/0x2e0 [snd_bcd2000]
[   50.727623] Read of size 8 at addr ffff88810fab0e88 by task swapper/4/0
[   50.729530] Call Trace:
[   50.732899]  bcd2000_input_complete+0x1f1/0x2e0 [snd_bcd2000]

Fix this by adding usb_kill_urb() before usb_free_urb().

Fixes: b47a22290d58 ("ALSA: MIDI driver for Behringer BCD2000 USB device")
Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
---
 sound/usb/bcd2000/bcd2000.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sound/usb/bcd2000/bcd2000.c b/sound/usb/bcd2000/bcd2000.c
index cd4a0bc6d278..7aec0a95c609 100644
--- a/sound/usb/bcd2000/bcd2000.c
+++ b/sound/usb/bcd2000/bcd2000.c
@@ -348,7 +348,8 @@ static int bcd2000_init_midi(struct bcd2000 *bcd2k)
 static void bcd2000_free_usb_related_resources(struct bcd2000 *bcd2k,
 						struct usb_interface *interface)
 {
-	/* usb_kill_urb not necessary, urb is aborted automatically */
+	usb_kill_urb(bcd2k->midi_out_urb);
+	usb_kill_urb(bcd2k->midi_in_urb);
 
 	usb_free_urb(bcd2k->midi_out_urb);
 	usb_free_urb(bcd2k->midi_in_urb);
-- 
2.25.1

Re: [PATCH] ALSA: bcd2000: Fix a UAF bug on the error path of probing

[Takashi Iwai]

On Fri, 15 Jul 2022 03:05:15 +0200,
Zheyu Ma wrote:
> 
> When the driver fails in snd_card_register() at probe time, it will free
> the 'bcd2k->midi_out_urb' before killing it, which may cause a UAF bug.
> 
> The following log can reveal it:
> 
> [   50.727020] BUG: KASAN: use-after-free in bcd2000_input_complete+0x1f1/0x2e0 [snd_bcd2000]
> [   50.727623] Read of size 8 at addr ffff88810fab0e88 by task swapper/4/0
> [   50.729530] Call Trace:
> [   50.732899]  bcd2000_input_complete+0x1f1/0x2e0 [snd_bcd2000]
> 
> Fix this by adding usb_kill_urb() before usb_free_urb().
> 
> Fixes: b47a22290d58 ("ALSA: MIDI driver for Behringer BCD2000 USB device")
> Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>

Thanks, applied.


Takashi