KMSAN: uninit-value in smsc75xx_bind

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: beaab8a3 fix KASAN build
git tree: kmsan
console output: https://syzkaller.appspot.com/x/log.txt?x=13d7b65c600000
kernel config: https://syzkaller.appspot.com/x/.config?x=4db781fe35a84ef5
dashboard link: https://syzkaller.appspot.com/bug?extid=6966546b78d050bb0b5d
compiler: clang version 9.0.0 (/home/glider/llvm/clang
80fee25776c2fb61e74c1ecb1a523375c2500b69)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14ab9ef0600000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11be2b34600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+696654...@syzkaller.appspotmail.com

==================================================================
BUG: KMSAN: uninit-value in smsc75xx_wait_ready
drivers/net/usb/smsc75xx.c:976 [inline]
BUG: KMSAN: uninit-value in smsc75xx_bind+0x541/0x12d0
drivers/net/usb/smsc75xx.c:1483
CPU: 0 PID: 2892 Comm: kworker/0:2 Not tainted 5.2.0+ #15
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: usb_hub_wq hub_event
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x191/0x1f0 lib/dump_stack.c:113
kmsan_report+0x162/0x2d0 mm/kmsan/kmsan_report.c:109
__msan_warning+0x75/0xe0 mm/kmsan/kmsan_instr.c:294
smsc75xx_wait_ready drivers/net/usb/smsc75xx.c:976 [inline]
smsc75xx_bind+0x541/0x12d0 drivers/net/usb/smsc75xx.c:1483
usbnet_probe+0x10d3/0x3950 drivers/net/usb/usbnet.c:1722
usb_probe_interface+0xd19/0x1310 drivers/usb/core/driver.c:361
really_probe+0x1344/0x1d90 drivers/base/dd.c:513
driver_probe_device+0x1ba/0x510 drivers/base/dd.c:670
__device_attach_driver+0x5b8/0x790 drivers/base/dd.c:777
bus_for_each_drv+0x28e/0x3b0 drivers/base/bus.c:454
__device_attach+0x489/0x750 drivers/base/dd.c:843
device_initial_probe+0x4a/0x60 drivers/base/dd.c:890
bus_probe_device+0x131/0x390 drivers/base/bus.c:514
device_add+0x25b5/0x2df0 drivers/base/core.c:2111
usb_set_configuration+0x309f/0x3710 drivers/usb/core/message.c:2027
generic_probe+0xe7/0x280 drivers/usb/core/generic.c:210
usb_probe_device+0x146/0x200 drivers/usb/core/driver.c:266
really_probe+0x1344/0x1d90 drivers/base/dd.c:513
driver_probe_device+0x1ba/0x510 drivers/base/dd.c:670
__device_attach_driver+0x5b8/0x790 drivers/base/dd.c:777
bus_for_each_drv+0x28e/0x3b0 drivers/base/bus.c:454
__device_attach+0x489/0x750 drivers/base/dd.c:843
device_initial_probe+0x4a/0x60 drivers/base/dd.c:890
bus_probe_device+0x131/0x390 drivers/base/bus.c:514
device_add+0x25b5/0x2df0 drivers/base/core.c:2111
usb_new_device+0x23e5/0x2fb0 drivers/usb/core/hub.c:2534
hub_port_connect drivers/usb/core/hub.c:5089 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5204 [inline]
port_event drivers/usb/core/hub.c:5350 [inline]
hub_event+0x5853/0x7320 drivers/usb/core/hub.c:5432
process_one_work+0x1572/0x1f00 kernel/workqueue.c:2269
process_scheduled_works kernel/workqueue.c:2331 [inline]
worker_thread+0x189c/0x2460 kernel/workqueue.c:2417
kthread+0x4b5/0x4f0 kernel/kthread.c:256
ret_from_fork+0x35/0x40 arch/x86/entry/entry_64.S:355

Local variable description: ----buf.i93@smsc75xx_bind
Variable was created at:
__smsc75xx_read_reg drivers/net/usb/smsc75xx.c:83 [inline]
smsc75xx_wait_ready drivers/net/usb/smsc75xx.c:969 [inline]
smsc75xx_bind+0x44c/0x12d0 drivers/net/usb/smsc75xx.c:1483
usbnet_probe+0x10d3/0x3950 drivers/net/usb/usbnet.c:1722
==================================================================


---
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[Oliver Neukum]

Am Freitag, den 09.08.2019, 01:48 -0700 schrieb syzbot:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: beaab8a3 fix KASAN build
> git tree: kmsan

[..]

> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x191/0x1f0 lib/dump_stack.c:113
> kmsan_report+0x162/0x2d0 mm/kmsan/kmsan_report.c:109
> __msan_warning+0x75/0xe0 mm/kmsan/kmsan_instr.c:294
> smsc75xx_wait_ready drivers/net/usb/smsc75xx.c:976 [inline]
> smsc75xx_bind+0x541/0x12d0 drivers/net/usb/smsc75xx.c:1483

>

> Local variable description: ----buf.i93@smsc75xx_bind
> Variable was created at:
> __smsc75xx_read_reg drivers/net/usb/smsc75xx.c:83 [inline]
> smsc75xx_wait_ready drivers/net/usb/smsc75xx.c:969 [inline]
> smsc75xx_bind+0x44c/0x12d0 drivers/net/usb/smsc75xx.c:1483
> usbnet_probe+0x10d3/0x3950 drivers/net/usb/usbnet.c:1722

Hi,

this looks like a false positive to me.
The offending code is likely this:

if (size) {
buf = kmalloc(size, GFP_KERNEL);
if (!buf)
goto out;
}

err = usb_control_msg(dev->udev, usb_rcvctrlpipe(dev->udev, 0),
cmd, reqtype, value, index, buf, size,
USB_CTRL_GET_TIMEOUT);

which uses 'buf' uninitialized. But it is used for input.
What is happening here?

Regards
Oliver

[Andrey Konovalov]

AFAICS, the uninitialized use of buf that KMSAN points out is in the
"if (buf & PMT_CTL_DEV_RDY)" statement in smsc75xx_wait_ready(). Does
__smsc75xx_read_reg/usb_control_msg() always initialize buf? Can it
just initialize the first few bytes for example?

[Oliver Neukum]

Hi,

you are unfortunately right and this is not the only driver vulnerable
in this way. I am going through them.

Regards
Oliver