[alsa-devel] [PATCH v2 3/9] ALSA: caiaq: Add a sanity check for invalid EPs

[Takashi Iwai]

On Wed, 11 Oct 2017 16:20:31 +0200,
Johan Hovold wrote:
> 
> On Wed, Oct 11, 2017 at 12:36:40PM +0200, Takashi Iwai wrote:
> > As syzkaller spotted, currently caiaq driver submits a URB with the
> > fixed EP without checking whether it's actually available, which may
> > result in a kernel warning like:
> >   usb 1-1: BOGUS urb xfer, pipe 3 != type 1
> >   ------------[ cut here ]------------
> >   WARNING: CPU: 1 PID: 1150 at drivers/usb/core/urb.c:449
> >   usb_submit_urb+0xf8a/0x11d0
> >   Modules linked in:
> >   CPU: 1 PID: 1150 Comm: kworker/1:1 Not tainted
> >   4.14.0-rc2-42660-g24b7bd59eec0 #277
> >   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> >   Workqueue: usb_hub_wq hub_event
> >   Call Trace:
> >    init_card sound/usb/caiaq/device.c:467
> >    snd_probe+0x81c/0x1150 sound/usb/caiaq/device.c:525
> >    usb_probe_interface+0x35d/0x8e0 drivers/usb/core/driver.c:361
> >    ....
> > 
> > This patch adds a sanity check of validity of EPs at the device
> > initialization phase for avoiding the call with an invalid EP.
> > 
> > Reported-by: Andrey Konovalov <andreyknvl at google.com>
> > Tested-by: Andrey Konovalov <andreyknvl at google.com>
> > Signed-off-by: Takashi Iwai <tiwai at suse.de>
> > ---
> >  sound/usb/caiaq/device.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/sound/usb/caiaq/device.c b/sound/usb/caiaq/device.c
> > index 0fb6b1b79261..a29674bf96e5 100644
> > --- a/sound/usb/caiaq/device.c
> > +++ b/sound/usb/caiaq/device.c
> > @@ -461,6 +461,13 @@ static int init_card(struct snd_usb_caiaqdev *cdev)
> >  			  cdev->midi_out_buf, EP1_BUFSIZE,
> >  			  snd_usb_caiaq_midi_output_done, cdev);
> >  
> > +	/* sanity checks of EPs before actually submitting */
> > +	if (usb_urb_ep_type_check(&cdev->ep1_in_urb) ||
> > +	    usb_urb_ep_type_check(&cdev->midi_out_urb)) {
> > +		dev_err(dev, "invalid EPs\n");
> > +		return -EINVAL;
> > +	}
> > +
> 
> Unrelated to this patch, but this driver fails to kill the ep1_in_urb
> (which is submitted in this function) in case of later probe errors.
> This can lead to use-after-free or crashes in the completion callback.

Yes, a good catch.  Below is the fix patch.


thanks,

Takashi

-- 8< --
From: Takashi Iwai <tiwai at suse.de>
Subject: [PATCH] ALSA: caiaq: Fix stray URB at probe error path

caiaq driver doesn't kill the URB properly at its error path during
the probe, which may lead to a use-after-free error later.  This patch
addresses it.

Reported-by: Johan Hovold <johan at kernel.org>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/usb/caiaq/device.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/sound/usb/caiaq/device.c b/sound/usb/caiaq/device.c
index a29674bf96e5..d55ca48de3ea 100644
--- a/sound/usb/caiaq/device.c
+++ b/sound/usb/caiaq/device.c
@@ -476,10 +476,12 @@ static int init_card(struct snd_usb_caiaqdev *cdev)
 
 	err = snd_usb_caiaq_send_command(cdev, EP1_CMD_GET_DEVICE_INFO, NULL, 0);
 	if (err)
-		return err;
+		goto err_kill_urb;
 
-	if (!wait_event_timeout(cdev->ep1_wait_queue, cdev->spec_received, HZ))
-		return -ENODEV;
+	if (!wait_event_timeout(cdev->ep1_wait_queue, cdev->spec_received, HZ)) {
+		err = -ENODEV;
+		goto err_kill_urb;
+	}
 
 	usb_string(usb_dev, usb_dev->descriptor.iManufacturer,
 		   cdev->vendor_name, CAIAQ_USB_STR_LEN);
@@ -514,6 +516,10 @@ static int init_card(struct snd_usb_caiaqdev *cdev)
 
 	setup_card(cdev);
 	return 0;
+
+ err_kill_urb:
+	usb_kill_urb(&cdev->ep1_in_urb);
+	return err;
 }
 
 static int snd_probe(struct usb_interface *intf,
-- 
2.14.2