Re: usb/sounds: slab-out-of-bounds read in snd_usb_create_streams

[Takashi Iwai <tiwai@suse.de>]

On Fri, 22 Sep 2017 15:55:17 +0200,
Andrey Konovalov wrote:
> 
> On Fri, Sep 22, 2017 at 3:19 PM, Takashi Iwai <tiwai@suse.de> wrote:
> > On Fri, 22 Sep 2017 14:56:06 +0200,
> > Andrey Konovalov wrote:
> >>
> >> Hi!
> >>
> >> I've got the following report while fuzzing the kernel with syzkaller.
> >>
> >> On commit ebb2c2437d8008d46796902ff390653822af6cc4 (Sep 18).
> >>
> >> It seems that there's no check that control_header has enough space
> >> for uac1_ac_header_descriptor in snd_usb_create_streams().
> >
> > Indeed, this might be an issue.
> > Does the patch below fix the problem?
> 
> I believe it does. It does fix the crash with my reproducer.
> 
> I'm not sure if the (rest_bytes <= 0) check is actually needed though.

It's superfluous, but safer is safer, and this check is cheap.

> It seems that if snd_usb_find_csint_desc() returns a non-null value,
> it'll always be within the buffer.
> 
> Tested-by: Andrey Konovalov <andreyknvl@google.com>

Thanks, I'm going to queue it.
FWIW, below is the official patch.


Takashi

-- 8< --
From: Takashi Iwai <tiwai@suse.de>
Subject: [PATCH] ALSA: usb-audio: Check out-of-bounds access by corrupted
 buffer descriptor

When a USB-audio device receives a maliciously adjusted or corrupted
buffer descriptor, the USB-audio driver may access an out-of-bounce
value at its parser.  This was detected by syzkaller, something like:

  BUG: KASAN: slab-out-of-bounds in usb_audio_probe+0x27b2/0x2ab0
  Read of size 1 at addr ffff88006b83a9e8 by task kworker/0:1/24
  CPU: 0 PID: 24 Comm: kworker/0:1 Not tainted 4.14.0-rc1-42251-gebb2c2437d80 #224
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
  Workqueue: usb_hub_wq hub_event
  Call Trace:
   __dump_stack lib/dump_stack.c:16
   dump_stack+0x292/0x395 lib/dump_stack.c:52
   print_address_description+0x78/0x280 mm/kasan/report.c:252
   kasan_report_error mm/kasan/report.c:351
   kasan_report+0x22f/0x340 mm/kasan/report.c:409
   __asan_report_load1_noabort+0x19/0x20 mm/kasan/report.c:427
   snd_usb_create_streams sound/usb/card.c:248
   usb_audio_probe+0x27b2/0x2ab0 sound/usb/card.c:605
   usb_probe_interface+0x35d/0x8e0 drivers/usb/core/driver.c:361
   really_probe drivers/base/dd.c:413
   driver_probe_device+0x610/0xa00 drivers/base/dd.c:557
   __device_attach_driver+0x230/0x290 drivers/base/dd.c:653
   bus_for_each_drv+0x161/0x210 drivers/base/bus.c:463
   __device_attach+0x26e/0x3d0 drivers/base/dd.c:710
   device_initial_probe+0x1f/0x30 drivers/base/dd.c:757
   bus_probe_device+0x1eb/0x290 drivers/base/bus.c:523
   device_add+0xd0b/0x1660 drivers/base/core.c:1835
   usb_set_configuration+0x104e/0x1870 drivers/usb/core/message.c:1932
   generic_probe+0x73/0xe0 drivers/usb/core/generic.c:174
   usb_probe_device+0xaf/0xe0 drivers/usb/core/driver.c:266
   really_probe drivers/base/dd.c:413
   driver_probe_device+0x610/0xa00 drivers/base/dd.c:557
   __device_attach_driver+0x230/0x290 drivers/base/dd.c:653
   bus_for_each_drv+0x161/0x210 drivers/base/bus.c:463
   __device_attach+0x26e/0x3d0 drivers/base/dd.c:710
   device_initial_probe+0x1f/0x30 drivers/base/dd.c:757
   bus_probe_device+0x1eb/0x290 drivers/base/bus.c:523
   device_add+0xd0b/0x1660 drivers/base/core.c:1835
   usb_new_device+0x7b8/0x1020 drivers/usb/core/hub.c:2457
   hub_port_connect drivers/usb/core/hub.c:4903
   hub_port_connect_change drivers/usb/core/hub.c:5009
   port_event drivers/usb/core/hub.c:5115
   hub_event+0x194d/0x3740 drivers/usb/core/hub.c:5195
   process_one_work+0xc7f/0x1db0 kernel/workqueue.c:2119
   worker_thread+0x221/0x1850 kernel/workqueue.c:2253
   kthread+0x3a1/0x470 kernel/kthread.c:231
   ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431

This patch adds the checks of out-of-bounce accesses at appropriate
places and bails out when it goes out of the given buffer.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/usb/card.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/sound/usb/card.c b/sound/usb/card.c
index 3dc36d913550..23d1d23aefec 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -221,6 +221,7 @@ static int snd_usb_create_streams(struct snd_usb_audio *chip, int ctrlif)
 	struct usb_interface_descriptor *altsd;
 	void *control_header;
 	int i, protocol;
+	int rest_bytes;
 
 	/* find audiocontrol interface */
 	host_iface = &usb_ifnum_to_if(dev, ctrlif)->altsetting[0];
@@ -235,6 +236,15 @@ static int snd_usb_create_streams(struct snd_usb_audio *chip, int ctrlif)
 		return -EINVAL;
 	}
 
+	rest_bytes = (void *)(host_iface->extra + host_iface->extralen) -
+		control_header;
+
+	/* just to be sure -- this shouldn't hit at all */
+	if (rest_bytes <= 0) {
+		dev_err(&dev->dev, "invalid control header\n");
+		return -EINVAL;
+	}
+
 	switch (protocol) {
 	default:
 		dev_warn(&dev->dev,
@@ -245,11 +255,21 @@ static int snd_usb_create_streams(struct snd_usb_audio *chip, int ctrlif)
 	case UAC_VERSION_1: {
 		struct uac1_ac_header_descriptor *h1 = control_header;
 
+		if (rest_bytes < sizeof(*h1)) {
+			dev_err(&dev->dev, "too short v1 buffer descriptor\n");
+			return -EINVAL;
+		}
+
 		if (!h1->bInCollection) {
 			dev_info(&dev->dev, "skipping empty audio interface (v1)\n");
 			return -EINVAL;
 		}
 
+		if (rest_bytes < h1->bLength) {
+			dev_err(&dev->dev, "invalid buffer length (v1)\n");
+			return -EINVAL;
+		}
+
 		if (h1->bLength < sizeof(*h1) + h1->bInCollection) {
 			dev_err(&dev->dev, "invalid UAC_HEADER (v1)\n");
 			return -EINVAL;
-- 
2.14.1