linux-kernel - Re: [Linux-kernel-mentees][PATCH] net: usb: rtl8150: prevent set_ethernet

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Message-ID: <20200929084752.GA8101@carbon>
Date:   Tue, 29 Sep 2020 11:47:52 +0300
From:   Petko Manolov <petko.manolov@...sulko.com>
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] net: usb: rtl8150: prevent
 set_ethernet_addr from setting uninit address

On 20-09-29 13:50:28, Anant Thazhemadam wrote:
> When get_registers() fails (which happens when usb_control_msg() fails)
> in set_ethernet_addr(), the uninitialized value of node_id gets copied
> as the address.
> 
> Checking for the return values appropriately, and handling the case
> wherein set_ethernet_addr() fails like this, helps in avoiding the
> mac address being incorrectly set in this manner.
> 
> 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 | 24 ++++++++++++++++--------
>  1 file changed, 16 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/usb/rtl8150.c b/drivers/net/usb/rtl8150.c
> index 733f120c852b..e542a9ab2ff8 100644
> --- a/drivers/net/usb/rtl8150.c
> +++ b/drivers/net/usb/rtl8150.c
> @@ -150,7 +150,7 @@ static const char driver_name [] = "rtl8150";
>  **	device related part of the code
>  **
>  */
> -static int get_registers(rtl8150_t * dev, u16 indx, u16 size, void *data)
> +static int get_registers(rtl8150_t *dev, u16 indx, u16 size, void *data)
>  {
>  	void *buf;
>  	int ret;
> @@ -274,12 +274,17 @@ static int write_mii_word(rtl8150_t * dev, u8 phy, __u8 indx, u16 reg)
>  		return 1;
>  }
>  
> -static inline void set_ethernet_addr(rtl8150_t * dev)
> +static bool set_ethernet_addr(rtl8150_t *dev)
>  {
>  	u8 node_id[6];
> +	int ret;
>  
> -	get_registers(dev, IDR, sizeof(node_id), node_id);
> -	memcpy(dev->netdev->dev_addr, node_id, sizeof(node_id));
> +	ret = get_registers(dev, IDR, sizeof(node_id), node_id);
> +	if (ret > 0 && ret <= sizeof(node_id)) {

get_registers() was recently modified to use usb_control_msg_recv() which does
not return partial reads.  IOW you'll either get negative value or
sizeof(node_id).  Since it is good to be paranoid i'd convert the above check
to:

	if (ret == sizeof(node_id)) {

and fail in any other case.  Apart from this minor detail the rest of the patch 
looks good to me.

Acked-by: Petko Manolov