net: usb: Fix uninit-was-stored issue in asix_read_phy_addr()

The buffer size is 2 Bytes and we expect to receive the same amount of
data. But sometimes we receive less data and run into uninit-was-stored
issue upon read. Hence modify the error check on the return value to match
with the buffer size as a prevention.

Reported-and-tested by: syzbot+a7e220df5a81d1ab400e@syzkaller.appspotmail.com
Signed-off-by: Himadri Pandya <himadrispandya@gmail.com>
---
 drivers/net/usb/asix_common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Hello!

On 27.08.2020 9:53, Himadri Pandya wrote:

> The buffer size is 2 Bytes and we expect to receive the same amount of
> data. But sometimes we receive less data and run into uninit-was-stored
> issue upon read. Hence modify the error check on the return value to match
> with the buffer size as a prevention.
> 
> Reported-and-tested by: syzbot+a7e220df5a81d1ab400e@syzkaller.appspotmail.com
> Signed-off-by: Himadri Pandya <himadrispandya@gmail.com>
> ---
>   drivers/net/usb/asix_common.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/usb/asix_common.c b/drivers/net/usb/asix_common.c
> index e39f41efda3e..7bc6e8f856fe 100644
> --- a/drivers/net/usb/asix_common.c
> +++ b/drivers/net/usb/asix_common.c
> @@ -296,7 +296,7 @@ int asix_read_phy_addr(struct usbnet *dev, int internal)
>   
>   	netdev_dbg(dev->net, "asix_get_phy_addr()\n");
>   
> -	if (ret < 0) {
> +	if (ret < 2) {
>   		netdev_err(dev->net, "Error reading PHYID register: %02x\n", ret);

    Hm... printing possibly negative values as hex?

[...]

MBR, Sergei

From: Himadri Pandya <himadrispandya@gmail.com>
Date: Thu, 27 Aug 2020 12:23:55 +0530

> The buffer size is 2 Bytes and we expect to receive the same amount of
> data. But sometimes we receive less data and run into uninit-was-stored
> issue upon read. Hence modify the error check on the return value to match
> with the buffer size as a prevention.
> 
> Reported-and-tested by: syzbot+a7e220df5a81d1ab400e@syzkaller.appspotmail.com
> Signed-off-by: Himadri Pandya <himadrispandya@gmail.com>

Applied, thanks.

On Thu, Aug 27, 2020 at 12:23:55PM +0530, Himadri Pandya wrote:
> The buffer size is 2 Bytes and we expect to receive the same amount of
> data. But sometimes we receive less data and run into uninit-was-stored
> issue upon read. Hence modify the error check on the return value to match
> with the buffer size as a prevention.
> 
> Reported-and-tested by: syzbot+a7e220df5a81d1ab400e@syzkaller.appspotmail.com
> Signed-off-by: Himadri Pandya <himadrispandya@gmail.com>
> ---
>  drivers/net/usb/asix_common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/usb/asix_common.c b/drivers/net/usb/asix_common.c
> index e39f41efda3e..7bc6e8f856fe 100644
> --- a/drivers/net/usb/asix_common.c
> +++ b/drivers/net/usb/asix_common.c
> @@ -296,7 +296,7 @@ int asix_read_phy_addr(struct usbnet *dev, int internal)
>  
>  	netdev_dbg(dev->net, "asix_get_phy_addr()\n");
>  
> -	if (ret < 0) {
> +	if (ret < 2) {
>  		netdev_err(dev->net, "Error reading PHYID register: %02x\n", ret);
>  		goto out;
>  	}

If ret is 0 or 1 here, shouldn't asix_read_phy_addr() return an error code
instead of 0 or 1?

- Eric

On Thu, Aug 27, 2020 at 1:28 PM Sergei Shtylyov
<sergei.shtylyov@gmail.com> wrote:
>
> Hello!
>
> On 27.08.2020 9:53, Himadri Pandya wrote:
>
> > The buffer size is 2 Bytes and we expect to receive the same amount of
> > data. But sometimes we receive less data and run into uninit-was-stored
> > issue upon read. Hence modify the error check on the return value to match
> > with the buffer size as a prevention.
> >
> > Reported-and-tested by: syzbot+a7e220df5a81d1ab400e@syzkaller.appspotmail.com
> > Signed-off-by: Himadri Pandya <himadrispandya@gmail.com>
> > ---
> >   drivers/net/usb/asix_common.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/usb/asix_common.c b/drivers/net/usb/asix_common.c
> > index e39f41efda3e..7bc6e8f856fe 100644
> > --- a/drivers/net/usb/asix_common.c
> > +++ b/drivers/net/usb/asix_common.c
> > @@ -296,7 +296,7 @@ int asix_read_phy_addr(struct usbnet *dev, int internal)
> >
> >       netdev_dbg(dev->net, "asix_get_phy_addr()\n");
> >
> > -     if (ret < 0) {
> > +     if (ret < 2) {
> >               netdev_err(dev->net, "Error reading PHYID register: %02x\n", ret);
>
>     Hm... printing possibly negative values as hex?
>

Yeah. That's odd! Fixing it.

Thanks,
Himadri

> [...]
>
> MBR, Sergei