usb/core: slab-out-of-bounds read in cdc_parse_cdc_header

[Andrey Konovalov]

Hi!

I've got the following crash while fuzzing the kernel with syzkaller.

On commit ebb2c2437d8008d46796902ff390653822af6cc4 (Sep 18).

It looks like cdc_parse_cdc_header() doesn't validate buflen before
accessing buffer[1], buffer[2] and so on. The only check present is
while (buflen > 0).

==================================================================
BUG: KASAN: slab-out-of-bounds in cdc_parse_cdc_header+0x611/0x6b0
Read of size 1 at addr ffff88006b03e554 by task kworker/1:2/2573

CPU: 1 PID: 2573 Comm: kworker/1:2 Not tainted 4.14.0-rc1+ #191
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+0x192/0x22c 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+0x230/0x340 mm/kasan/report.c:409
__asan_report_load1_noabort+0x19/0x20 mm/kasan/report.c:427
cdc_parse_cdc_header+0x611/0x6b0 drivers/usb/core/message.c:2077
usbnet_generic_cdc_bind+0x284/0x1b10 drivers/net/usb/cdc_ether.c:158
usbnet_ether_cdc_bind drivers/net/usb/cdc_ether.c:329
usbnet_cdc_bind+0x2a/0x190 drivers/net/usb/cdc_ether.c:437
usbnet_probe+0xcfd/0x2ba0 drivers/net/usb/usbnet.c:1726
usb_probe_interface+0x351/0x8d0 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+0x15e/0x210 drivers/base/bus.c:463
__device_attach+0x269/0x3c0 drivers/base/dd.c:710
device_initial_probe+0x1f/0x30 drivers/base/dd.c:757
bus_probe_device+0x1da/0x280 drivers/base/bus.c:523
device_add+0xcf9/0x1640 drivers/base/core.c:1835
usb_set_configuration+0x1064/0x1890 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+0x15e/0x210 drivers/base/bus.c:463
__device_attach+0x269/0x3c0 drivers/base/dd.c:710
device_initial_probe+0x1f/0x30 drivers/base/dd.c:757
bus_probe_device+0x1da/0x280 drivers/base/bus.c:523
device_add+0xcf9/0x1640 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+0x23c8/0x37c0 drivers/usb/core/hub.c:5195
process_one_work+0x9fb/0x1570 kernel/workqueue.c:2119
worker_thread+0x1e4/0x1350 kernel/workqueue.c:2253
kthread+0x324/0x3f0 kernel/kthread.c:231
ret_from_fork+0x25/0x30 arch/x86/entry/entry_64.S:431

Allocated by task 2573:
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+0x81/0x1d0 mm/slub.c:3782
kmalloc ./include/linux/slab.h:498
usb_get_configuration+0x372/0x2a70 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+0x23c8/0x37c0 drivers/usb/core/hub.c:5195
process_one_work+0x9fb/0x1570 kernel/workqueue.c:2119
worker_thread+0x1e4/0x1350 kernel/workqueue.c:2253
kthread+0x324/0x3f0 kernel/kthread.c:231
ret_from_fork+0x25/0x30 arch/x86/entry/entry_64.S:43

Freed by task 3637:
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+0x96/0x1a0 mm/slub.c:3919
kvfree+0x3b/0x60 mm/util.c:416
__vunmap+0x1de/0x270 mm/vmalloc.c:1542
vfree+0x55/0xe0 mm/vmalloc.c:1606
n_tty_close+0xb7/0x120 drivers/tty/n_tty.c:1864
tty_ldisc_close.isra.0+0x9e/0xd0 drivers/tty/tty_ldisc.c:490
tty_ldisc_kill+0x4a/0xc0 drivers/tty/tty_ldisc.c:639
tty_ldisc_release+0x10b/0x220 drivers/tty/tty_ldisc.c:807
tty_release_struct+0x1f/0x50 drivers/tty/tty_io.c:1571
tty_release+0xe60/0x15f0 drivers/tty/tty_io.c:1744
__fput+0x324/0x7e0 fs/file_table.c:210
____fput+0x1a/0x20 fs/file_table.c:244
task_work_run+0x22e/0x2e0 kernel/task_work.c:112
tracehook_notify_resume ./include/linux/tracehook.h:191
exit_to_usermode_loop+0x1d7/0x210 arch/x86/entry/common.c:162
prepare_exit_to_usermode arch/x86/entry/common.c:197
syscall_return_slowpath+0x2a7/0x310 arch/x86/entry/common.c:266
entry_SYSCALL_64_fastpath+0xa3/0xa5 arch/x86/entry/entry_64.S:238

The buggy address belongs to the object at ffff88006b03e540
which belongs to the cache kmalloc-32 of size 32
The buggy address is located 20 bytes inside of
32-byte region [ffff88006b03e540, ffff88006b03e560)
The buggy address belongs to the page:
page:ffffea0001ac0f80 count:1 mapcount:0 mapping: (null) index:0x0
flags: 0x100000000000100(slab)
raw: 0100000000000100 0000000000000000 0000000000000000 0000000180550055
raw: ffffea0001a92340 0000000200000002 ffff88006c401a00 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88006b03e400: 00 00 fc fc 00 00 00 fc fc fc fb fb fb fb fc fc
ffff88006b03e480: fb fb fb fb fc fc fb fb fb fb fc fc fb fb fb fb
>ffff88006b03e500: fc fc fb fb fb fb fc fc 00 00 04 fc fc fc fb fb
^
ffff88006b03e580: fb fb fc fc fb fb fb fb fc fc fb fb fb fb fc fc
ffff88006b03e600: fb fb fb fb fc fc fb fb fb fb fc fc fb fb fb fb
==================================================================

[Greg Kroah-Hartman]

On Wed, Sep 20, 2017 at 04:45:08PM +0200, Andrey Konovalov wrote:
> Hi!
>
> I've got the following crash while fuzzing the kernel with syzkaller.
>
> On commit ebb2c2437d8008d46796902ff390653822af6cc4 (Sep 18).
>
> It looks like cdc_parse_cdc_header() doesn't validate buflen before
> accessing buffer[1], buffer[2] and so on. The only check present is
> while (buflen > 0).

Ugh, you are right, let me go work on a patch, thanks for the report...

[Greg Kroah-Hartman]

Here's a first cut at a fix for this. I think this should solve it, but
it's early and my coffee has not fully kicked in...

thanks,

greg k-h
-----------------

diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index 4c38ea41ae96..028feaf01aa5 100644
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -2069,6 +2069,10 @@ int cdc_parse_cdc_header(struct usb_cdc_parsed_header *hdr,
elength = 1;
goto next_desc;
}
+ if ((buflen < elength) || (elength < 2)) {
+ dev_err(&intf->dev, "invalid descriptor buffer length\n");
+ break;
+ }
if (buffer[1] != USB_DT_CS_INTERFACE) {
dev_err(&intf->dev, "skipping garbage\n");
goto next_desc;

[Andrey Konovalov]

On Thu, Sep 21, 2017 at 10:04 AM, Greg Kroah-Hartman
<gre...@linuxfoundation.org> wrote:
> On Thu, Sep 21, 2017 at 09:31:54AM +0200, Greg Kroah-Hartman wrote:
>> On Wed, Sep 20, 2017 at 04:45:08PM +0200, Andrey Konovalov wrote:
>> > Hi!
>> >
>> > I've got the following crash while fuzzing the kernel with syzkaller.
>> >
>> > On commit ebb2c2437d8008d46796902ff390653822af6cc4 (Sep 18).
>> >
>> > It looks like cdc_parse_cdc_header() doesn't validate buflen before
>> > accessing buffer[1], buffer[2] and so on. The only check present is
>> > while (buflen > 0).
>>
>> Ugh, you are right, let me go work on a patch, thanks for the report...
>
> Here's a first cut at a fix for this. I think this should solve it, but
> it's early and my coffee has not fully kicked in...
>
> thanks,
>
> greg k-h
> -----------------
>
> diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
> index 4c38ea41ae96..028feaf01aa5 100644
> --- a/drivers/usb/core/message.c
> +++ b/drivers/usb/core/message.c
> @@ -2069,6 +2069,10 @@ int cdc_parse_cdc_header(struct usb_cdc_parsed_header *hdr,
> elength = 1;
> goto next_desc;
> }
> + if ((buflen < elength) || (elength < 2)) {

Hi Greg,

I think this should check (elength < 3), since we access both
buffer[1] and buffer[2] after this check.

Thanks!

> + dev_err(&intf->dev, "invalid descriptor buffer length\n");
> + break;
> + }
> if (buffer[1] != USB_DT_CS_INTERFACE) {
> dev_err(&intf->dev, "skipping garbage\n");
> goto next_desc;
>

> --
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[Greg Kroah-Hartman]

{sigh} yes, you are right, counted this one wrong.

With this patch, updated one below, does it fix your crash?

thanks,

greg k-h

diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index 4c38ea41ae96..028feaf01aa5 100644
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -2069,6 +2069,10 @@ int cdc_parse_cdc_header(struct usb_cdc_parsed_header *hdr,
elength = 1;
goto next_desc;
}

+ if ((buflen < elength) || (elength < 3)) {

[Andrey Konovalov]

On Thu, Sep 21, 2017 at 4:07 PM, Greg Kroah-Hartman

It does, thanks!

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