[Linux-kernel-mentees] [PATCH] usb: asix: Fix uninit-value in asix_mdio_write

[Linux-kernel-mentees] [PATCH] usb: asix: Fix uninit-value in asix_mdio_write

[Phong Tran]

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

Reported-by: syzbot+7dc7c28d4577bbe55b10@syzkaller.appspotmail.com

Test result:

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

Signed-off-by: Phong Tran <tranmanphong@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

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Re: [Linux-kernel-mentees] [PATCH] usb: asix: Fix uninit-value in asix_mdio_write

[David Miller]

From: Phong Tran <tranmanphong@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+7dc7c28d4577bbe55b10@syzkaller.appspotmail.com
> 
> Test result:
> 
> https://groups.google.com/d/msg/syzkaller-bugs/3H_n05x_sPU/sUoHhxgAAgAJ
> 
> Signed-off-by: Phong Tran <tranmanphong@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.
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[Linux-kernel-mentees] [[Patch V2]] usb: asix: cleanup the buffer in asix_read_cmd

[Phong Tran]

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

Reported-by: syzbot+7dc7c28d4577bbe55b10@syzkaller.appspotmail.com

Tested by:

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

Signed-off-by: Phong Tran <tranmanphong@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

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Re: [Linux-kernel-mentees] [PATCH] usb: asix: Fix uninit-value in asix_mdio_write

[Phong Tran]

On 11/8/19 6:21 AM, David Miller wrote:
> From: Phong Tran <tranmanphong@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+7dc7c28d4577bbe55b10@syzkaller.appspotmail.com
>>
>> Test result:
>>
>> https://groups.google.com/d/msg/syzkaller-bugs/3H_n05x_sPU/sUoHhxgAAgAJ
>>
>> Signed-off-by: Phong Tran <tranmanphong@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.
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