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Message-ID: <87h6nmegt9.wl-tiwai@suse.de>
Date: Fri, 22 Sep 2023 10:46:26 +0200
From: Takashi Iwai <tiwai@...e.de>
To: "Ricardo B. Marliere" <ricardo@...liere.net>
Cc: Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
Ruslan Bilovol <ruslan.bilovol@...il.com>,
alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
linux-kernel-mentees@...ts.linuxfoundation.org,
syzbot+59875ffef5cb9c9b29e9@...kaller.appspotmail.com
Subject: Re: [PATCH] sound: usb: increase snd_card alloc size
On Fri, 22 Sep 2023 02:51:53 +0200,
Ricardo B. Marliere wrote:
>
> Syzbot reports a slab-out-of-bounds read of a snd_card object. When
> snd_usb_audio_create calls snd_card_new, it passes sizeof(*chip) as the
> extra_size argument, which is not enough in this case.
>
> Relevant logs below:
>
> BUG: KASAN: slab-out-of-bounds in imon_probe+0x2983/0x3910
> Read of size 1 at addr ffff8880436a2c71 by task kworker/1:2/777
> (...)
> The buggy address belongs to the object at ffff8880436a2000
> which belongs to the cache kmalloc-4k of size 4096
> The buggy address is located 1 bytes to the right of
> allocated 3184-byte region [ffff8880436a2000, ffff8880436a2c70)
>
> Reported-by: syzbot+59875ffef5cb9c9b29e9@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/all/000000000000a838aa0603cc74d6@google.co/m
> Signed-off-by: Ricardo B. Marliere <ricardo@...liere.net>
> ---
> sound/usb/card.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/sound/usb/card.c b/sound/usb/card.c
> index 1b2edc0fd2e9..6578326d33e8 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -619,7 +619,7 @@ static int snd_usb_audio_create(struct usb_interface *intf,
> }
>
> err = snd_card_new(&intf->dev, index[idx], id[idx], THIS_MODULE,
> - sizeof(*chip), &card);
> + sizeof(*chip) + 2, &card);
Sorry, it's no-no. We have to fix the cause of the OOB access instead
of papering over with a random number of increase.
Unfortunately, most important piece of information is trimmed in the
changelog, so I can't judge what's going on. The only useful info
there is that it's something to do with imon driver, but it's
completely independent from USB-audio. How does it access to the
external memory allocated by snd-usb-audio driver at all?
Before jumping to the solution, we must understand the problem.
thanks,
Takashi
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