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

[Andrey Konovalov]

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().

==================================================================
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

Allocated by task 24:
save_stack_trace+0x1b/0x20 arch/x86/kernel/stacktrace.c:59
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459
kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
__kmalloc+0x14e/0x310 mm/slub.c:3782
kmalloc ./include/linux/slab.h:498
usb_get_configuration+0x372/0x2a60 drivers/usb/core/config.c:848
usb_enumerate_device drivers/usb/core/hub.c:2290
usb_new_device+0xaae/0x1020 drivers/usb/core/hub.c:2426
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

Freed by task 4048:
save_stack_trace+0x1b/0x20 arch/x86/kernel/stacktrace.c:59
save_stack+0x43/0xd0 mm/kasan/kasan.c:447
set_track mm/kasan/kasan.c:459
kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:524
slab_free_hook mm/slub.c:1390
slab_free_freelist_hook mm/slub.c:1412
slab_free mm/slub.c:2988
kfree+0xf6/0x2f0 mm/slub.c:3919
free_rb_tree_fname+0x8a/0xe0 fs/ext4/dir.c:402
ext4_htree_free_dir_info fs/ext4/dir.c:424
ext4_release_dir+0x49/0x70 fs/ext4/dir.c:622
__fput+0x33e/0x800 fs/file_table.c:210
____fput+0x1a/0x20 fs/file_table.c:244
task_work_run+0x1af/0x280 kernel/task_work.c:112
tracehook_notify_resume ./include/linux/tracehook.h:191
exit_to_usermode_loop+0x1e1/0x220 arch/x86/entry/common.c:162
prepare_exit_to_usermode arch/x86/entry/common.c:197
syscall_return_slowpath+0x414/0x480 arch/x86/entry/common.c:266
entry_SYSCALL_64_fastpath+0xc0/0xc2 arch/x86/entry/entry_64.S:238

The buggy address belongs to the object at ffff88006b83a9c0
which belongs to the cache kmalloc-64 of size 64
The buggy address is located 40 bytes inside of
64-byte region [ffff88006b83a9c0, ffff88006b83aa00)
The buggy address belongs to the page:
page:ffffea0001ae0e80 count:1 mapcount:0 mapping: (null) index:0x0
flags: 0x100000000000100(slab)
raw: 0100000000000100 0000000000000000 0000000000000000 00000001802a002a
raw: 0000000000000000 0000000100000001 ffff88006c403800 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88006b83a880: fc fc fc fc 00 00 00 00 00 00 00 00 fc fc fc fc
ffff88006b83a900: fb fb fb fb fb fb fb fb fc fc fc fc 00 00 00 00
>ffff88006b83a980: 00 00 fc fc fc fc fc fc 00 00 00 00 07 fc fc fc
^
ffff88006b83aa00: fc fc fc fc 00 00 00 00 00 00 00 00 fc fc fc fc
ffff88006b83aa80: 00 00 00 00 00 00 00 00 fc fc fc fc 00 00 00 00
==================================================================

[Takashi Iwai]

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?


Takashi

---
diff --git a/sound/usb/card.c b/sound/usb/card.c
index 3dc36d913550..fc969efbb37c 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 +236,13 @@ 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;
+ if (rest_bytes <= 0) {
+ dev_err(&dev->dev, "invalid control header\n");
+ return -EINVAL;
+ }
+
switch (protocol) {
default:
dev_warn(&dev->dev,
@@ -245,11 +253,21 @@ 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;

[Andrey Konovalov]

On Fri, Sep 22, 2017 at 3:19 PM, Takashi Iwai <ti...@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 seems that if snd_usb_find_csint_desc() returns a non-null value,
it'll always be within the buffer.

Tested-by: Andrey Konovalov <andre...@google.com>

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[Takashi Iwai]

On Fri, 22 Sep 2017 15:55:17 +0200,
Andrey Konovalov wrote:
>
> On Fri, Sep 22, 2017 at 3:19 PM, Takashi Iwai <ti...@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 <andre...@google.com>

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


Takashi

-- 8< --
From: Takashi Iwai <ti...@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:

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 <andre...@google.com>
Tested-by: Andrey Konovalov <andre...@google.com>
Cc: <sta...@vger.kernel.org>
Signed-off-by: Takashi Iwai <ti...@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