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Date:   Wed, 16 Sep 2020 08:22:27 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Anant Thazhemadam <anant.thazhemadam@...il.com>
Cc:     linux-kernel-mentees@...ts.linuxfoundation.org,
        syzbot+abbc768b560c84d92fd3@...kaller.appspotmail.com,
        Petko Manolov <petkan@...leusys.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-usb@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Linux-kernel-mentees][PATCH] rtl8150: set memory to all 0xFFs
 on failed register reads

On Wed, Sep 16, 2020 at 10:35:40AM +0530, Anant Thazhemadam wrote:
> get_registers() copies whatever memory is written by the
> usb_control_msg() call even if the underlying urb call ends up failing.
> 
> If get_registers() fails, or ends up reading 0 bytes, meaningless and 
> junk register values would end up being copied over (and eventually read 
> by the driver), and since most of the callers of get_registers() don't 
> check the return values of get_registers() either, this would go unnoticed.
> 
> It might be a better idea to try and mirror the PCI master abort
> termination and set memory to 0xFFs instead in such cases.

It would be better to use this new api call instead of
usb_control_msg():
	https://lore.kernel.org/r/20200914153756.3412156-1-gregkh@linuxfoundation.org

How about porting this patch to run on top of that series instead?  That
should make this logic much simpler.



> 
> Fixes: https://syzkaller.appspot.com/bug?extid=abbc768b560c84d92fd3
> Reported-by: syzbot+abbc768b560c84d92fd3@...kaller.appspotmail.com
> Tested-by: syzbot+abbc768b560c84d92fd3@...kaller.appspotmail.com
> Signed-off-by: Anant Thazhemadam <anant.thazhemadam@...il.com>
> ---
>  drivers/net/usb/rtl8150.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/usb/rtl8150.c b/drivers/net/usb/rtl8150.c
> index 733f120c852b..04fca7bfcbcb 100644
> --- a/drivers/net/usb/rtl8150.c
> +++ b/drivers/net/usb/rtl8150.c
> @@ -162,8 +162,13 @@ static int get_registers(rtl8150_t * dev, u16 indx, u16 size, void *data)
>  	ret = usb_control_msg(dev->udev, usb_rcvctrlpipe(dev->udev, 0),
>  			      RTL8150_REQ_GET_REGS, RTL8150_REQT_READ,
>  			      indx, 0, buf, size, 500);
> -	if (ret > 0 && ret <= size)
> +
> +	if (ret < 0)
> +		memset(data, 0xff, size);
> +
> +	else
>  		memcpy(data, buf, ret);
> +
>  	kfree(buf);
>  	return ret;
>  }
> @@ -276,7 +281,7 @@ static int write_mii_word(rtl8150_t * dev, u8 phy, __u8 indx, u16 reg)
>  
>  static inline void set_ethernet_addr(rtl8150_t * dev)
>  {
> -	u8 node_id[6];
> +	u8 node_id[6] = {0};

This should not be needed to be done.

thanks,

greg k-h

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