KMSAN: uninit-value in asix_mdio_write

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: c2453450 kmsan: kcov: prettify the code unpoisoning area->..
git tree: https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=1159ab53600000
kernel config: https://syzkaller.appspot.com/x/.config?x=3684f3c73f43899a
dashboard link: https://syzkaller.appspot.com/bug?extid=7dc7c28d4577bbe55b10
compiler: clang version 9.0.0 (/home/glider/llvm/clang
80fee25776c2fb61e74c1ecb1a523375c2500b69)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17e7276f600000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15609b30e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+7dc7c2...@syzkaller.appspotmail.com

asix 1-1:0.145 (unnamed net_device) (uninitialized): Failed to enable
software MII access
asix 1-1:0.145 (unnamed net_device) (uninitialized): Failed to read reg
index 0x0000: -71
=====================================================
BUG: KMSAN: uninit-value in asix_mdio_write+0x3fa/0x8d0
drivers/net/usb/asix_common.c:496
CPU: 1 PID: 17 Comm: kworker/1:0 Not tainted 5.4.0-rc3+ #0
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+0x14a/0x2f0 mm/kmsan/kmsan_report.c:109
__msan_warning+0x73/0xf0 mm/kmsan/kmsan_instr.c:245
asix_mdio_write+0x3fa/0x8d0 drivers/net/usb/asix_common.c:496
asix_phy_reset+0xd8/0x2d0 drivers/net/usb/asix_devices.c:208
ax88172_bind+0x780/0xbd0 drivers/net/usb/asix_devices.c:272
usbnet_probe+0x10d3/0x39d0 drivers/net/usb/usbnet.c:1730
usb_probe_interface+0xd19/0x1310 drivers/usb/core/driver.c:361
really_probe+0xd91/0x1f90 drivers/base/dd.c:552
driver_probe_device+0x1ba/0x510 drivers/base/dd.c:721
__device_attach_driver+0x5b8/0x790 drivers/base/dd.c:828
bus_for_each_drv+0x28e/0x3b0 drivers/base/bus.c:430
__device_attach+0x489/0x750 drivers/base/dd.c:894
device_initial_probe+0x4a/0x60 drivers/base/dd.c:941
bus_probe_device+0x131/0x390 drivers/base/bus.c:490
device_add+0x25b5/0x2df0 drivers/base/core.c:2201
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+0xd91/0x1f90 drivers/base/dd.c:552
driver_probe_device+0x1ba/0x510 drivers/base/dd.c:721
__device_attach_driver+0x5b8/0x790 drivers/base/dd.c:828
bus_for_each_drv+0x28e/0x3b0 drivers/base/bus.c:430
__device_attach+0x489/0x750 drivers/base/dd.c:894
device_initial_probe+0x4a/0x60 drivers/base/dd.c:941
bus_probe_device+0x131/0x390 drivers/base/bus.c:490
device_add+0x25b5/0x2df0 drivers/base/core.c:2201
usb_new_device+0x23e5/0x2fb0 drivers/usb/core/hub.c:2536
hub_port_connect drivers/usb/core/hub.c:5098 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5213 [inline]
port_event drivers/usb/core/hub.c:5359 [inline]
hub_event+0x581d/0x72f0 drivers/usb/core/hub.c:5441
process_one_work+0x1572/0x1ef0 kernel/workqueue.c:2269
worker_thread+0x111b/0x2460 kernel/workqueue.c:2415
kthread+0x4b5/0x4f0 kernel/kthread.c:256
ret_from_fork+0x35/0x40 arch/x86/entry/entry_64.S:355

Local variable description: ----smsr@asix_mdio_write
Variable was created at:
asix_mdio_write+0xc7/0x8d0 drivers/net/usb/asix_common.c:480
asix_mdio_write+0xc7/0x8d0 drivers/net/usb/asix_common.c:480
=====================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Phong Tran]

The local variables use without initilization value.
This fixes the syzbot report.

Reported-by: syzbot+7dc7c2...@syzkaller.appspotmail.com

Test result:

https://groups.google.com/d/msg/syzkaller-bugs/3H_n05x_sPU/sUoHhxgAAgAJ

Signed-off-by: Phong Tran <tranma...@gmail.com>
---
drivers/net/usb/asix_common.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/net/usb/asix_common.c b/drivers/net/usb/asix_common.c
index e39f41efda3e..3c7ccd8a9da8 100644
--- a/drivers/net/usb/asix_common.c
+++ b/drivers/net/usb/asix_common.c
@@ -444,8 +444,8 @@ void asix_set_multicast(struct net_device *net)
int asix_mdio_read(struct net_device *netdev, int phy_id, int loc)
{
struct usbnet *dev = netdev_priv(netdev);
- __le16 res;
- u8 smsr;
+ __le16 res = 0;
+ u8 smsr = 0;
int i = 0;
int ret;

@@ -478,7 +478,7 @@ void asix_mdio_write(struct net_device *netdev, int phy_id, int loc, int val)
{
struct usbnet *dev = netdev_priv(netdev);
__le16 res = cpu_to_le16(val);
- u8 smsr;
+ u8 smsr = 0;
int i = 0;
int ret;

@@ -508,8 +508,8 @@ void asix_mdio_write(struct net_device *netdev, int phy_id, int loc, int val)
int asix_mdio_read_nopm(struct net_device *netdev, int phy_id, int loc)
{
struct usbnet *dev = netdev_priv(netdev);
- __le16 res;
- u8 smsr;
+ __le16 res = 0;
+ u8 smsr = 0;
int i = 0;
int ret;

@@ -543,7 +543,7 @@ asix_mdio_write_nopm(struct net_device *netdev, int phy_id, int loc, int val)
{
struct usbnet *dev = netdev_priv(netdev);
__le16 res = cpu_to_le16(val);
- u8 smsr;
+ u8 smsr = 0;
int i = 0;
int ret;

--
2.20.1

[David Miller]

From: Phong Tran <tranma...@gmail.com>
Date: Thu, 7 Nov 2019 07:44:04 +0700

> The local variables use without initilization value.
> This fixes the syzbot report.
>
> Reported-by: syzbot+7dc7c2...@syzkaller.appspotmail.com
>
> Test result:
>
> https://groups.google.com/d/msg/syzkaller-bugs/3H_n05x_sPU/sUoHhxgAAgAJ
>
> Signed-off-by: Phong Tran <tranma...@gmail.com>

There are several more situations in this file where the data blob passed
to asix_read_cmd() is read without pre-initialization not checking the
return value from asix_read_cmd().

So, syzbot can see some of them but not all of them, yet all of them
are buggy and should be fixed.

These kinds of patches drive me absolutely crazy :-)

Really, one of two things needs to happen, either asix_read_cmd() clears
the incoming buffer unconditionally, or these call sites strictly must
check the return value always before accessing the buffer after the call.

I'm not applying this, sorry.

[Phong Tran]

This is for fixing KMSAN: uninit-value in asix_mdio_write
comes from syzbot.

Reported-by: syzbot+7dc7c2...@syzkaller.appspotmail.com

Tested by:

https://groups.google.com/d/msg/syzkaller-bugs/3H_n05x_sPU/07UIX_TUEgAJ

Signed-off-by: Phong Tran <tranma...@gmail.com>
---

drivers/net/usb/asix_common.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/net/usb/asix_common.c b/drivers/net/usb/asix_common.c
index e39f41efda3e..f3eeb7875a4d 100644
--- a/drivers/net/usb/asix_common.c
+++ b/drivers/net/usb/asix_common.c
@@ -22,6 +22,8 @@ int asix_read_cmd(struct usbnet *dev, u8 cmd, u16 value, u16 index,
else
fn = usbnet_read_cmd_nopm;

+ memset(data, 0, size);
+
ret = fn(dev, cmd, USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
value, index, data, size);

--
2.20.1

[Phong Tran]

On 11/8/19 6:21 AM, David Miller wrote:
> From: Phong Tran <tranma...@gmail.com>
> Date: Thu, 7 Nov 2019 07:44:04 +0700
>
>> The local variables use without initilization value.
>> This fixes the syzbot report.
>>
>> Reported-by: syzbot+7dc7c2...@syzkaller.appspotmail.com
>>
>> Test result:
>>
>> https://groups.google.com/d/msg/syzkaller-bugs/3H_n05x_sPU/sUoHhxgAAgAJ
>>
>> Signed-off-by: Phong Tran <tranma...@gmail.com>
>
> There are several more situations in this file where the data blob passed
> to asix_read_cmd() is read without pre-initialization not checking the
> return value from asix_read_cmd().
>
> So, syzbot can see some of them but not all of them, yet all of them
> are buggy and should be fixed.
>
> These kinds of patches drive me absolutely crazy :-)
>
> Really, one of two things needs to happen, either asix_read_cmd() clears
> the incoming buffer unconditionally,

thank you for your suggestion.
Sent Patch v2 reply-to this mail thread.

regards,
Phong.

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.