2019-04-29 17:48:20

by Wenwen Wang

Subject: [PATCH v2] ALSA: usx2y: fix a double free bug

In usX2Y_In04_init(), a new urb is firstly created through usb_alloc_urb()
and saved to 'usX2Y->In04urb'. Then, a buffer is allocated through
kmalloc() and saved to 'usX2Y->In04Buf'. If the allocation of the buffer
fails, the error code ENOMEM is returned after usb_free_urb(), which frees
the created urb. However, the urb is actually freed at card->private_free
callback, i.e., snd_usX2Y_card_private_free(). So the free operation here
leads to a double free bug.

To fix the above issue, simply remove usb_free_urb().

Signed-off-by: Wenwen Wang <[email protected]>
---
sound/usb/usx2y/usbusx2y.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/sound/usb/usx2y/usbusx2y.c b/sound/usb/usx2y/usbusx2y.c
index da4a5a5..1f0b0100 100644
--- a/sound/usb/usx2y/usbusx2y.c
+++ b/sound/usb/usx2y/usbusx2y.c
@@ -293,10 +293,8 @@ int usX2Y_In04_init(struct usX2Ydev *usX2Y)
if (! (usX2Y->In04urb = usb_alloc_urb(0, GFP_KERNEL)))
return -ENOMEM;

- if (! (usX2Y->In04Buf = kmalloc(21, GFP_KERNEL))) {
- usb_free_urb(usX2Y->In04urb);
+ if (! (usX2Y->In04Buf = kmalloc(21, GFP_KERNEL)))
return -ENOMEM;
- }

init_waitqueue_head(&usX2Y->In04WaitQueue);
usb_fill_int_urb(usX2Y->In04urb, usX2Y->dev, usb_rcvintpipe(usX2Y->dev, 0x4),
--
2.7.4

2019-04-29 17:58:58

by Takashi Iwai

Subject: Re: [PATCH v2] ALSA: usx2y: fix a double free bug

On Mon, 29 Apr 2019 19:45:40 +0200,
Wenwen Wang wrote:
>
> In usX2Y_In04_init(), a new urb is firstly created through usb_alloc_urb()
> and saved to 'usX2Y->In04urb'. Then, a buffer is allocated through
> kmalloc() and saved to 'usX2Y->In04Buf'. If the allocation of the buffer
> fails, the error code ENOMEM is returned after usb_free_urb(), which frees
> the created urb. However, the urb is actually freed at card->private_free
> callback, i.e., snd_usX2Y_card_private_free(). So the free operation here
> leads to a double free bug.
>
> To fix the above issue, simply remove usb_free_urb().
>
> Signed-off-by: Wenwen Wang <[email protected]>

Applied now. Thanks.


Takashi