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Subject: Re: [Linux-kernel-mentees][PATCH] rtl8150: set memory to all 0xFFs on
 failed register reads
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     linux-kernel-mentees@lists.linuxfoundation.org,
        syzbot+abbc768b560c84d92fd3@syzkaller.appspotmail.com,
        Petko Manolov <petkan@nucleusys.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, linux-usb@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20200916050540.15290-1-anant.thazhemadam@gmail.com>
 <20200916062227.GD142621@kroah.com>
From:   Anant Thazhemadam <anant.thazhemadam@gmail.com>
Message-ID: <dfdb48b8-5cd9-2b19-11cc-b17f45904e0f@gmail.com>
Date:   Wed, 16 Sep 2020 19:10:55 +0530
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On 16/09/20 11:52 am, Greg KH wrote:
> 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.
This looks viable to me. I'll be sure to try this out.
>> Fixes: https://syzkaller.appspot.com/bug?extid=abbc768b560c84d92fd3
>> Reported-by: syzbot+abbc768b560c84d92fd3@syzkaller.appspotmail.com
>> Tested-by: syzbot+abbc768b560c84d92fd3@syzkaller.appspotmail.com
>> Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.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.

Noted.

Thank you for your time.

Thanks,
Anant