Re: [PATCH net-next] net: asix: add proper error handling of usb read errors

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Feb 06, 2022 at 09:05:16PM +0300, Pavel Skripkin wrote:
> Syzbot once again hit uninit value in asix driver. The problem still the
> same -- asix_read_cmd() reads less bytes, than was requested by caller.
> 
> Since all read requests are performed via asix_read_cmd() let's catch
> usb related error there and add __must_check notation to be sure all
> callers actually check return value.
> 
> So, this patch adds sanity check inside asix_read_cmd(), that simply
> checks if bytes read are not less, than was requested and adds missing
> error handling of asix_read_cmd() all across the driver code.
> 
> Fixes: d9fe64e51114 ("net: asix: Add in_pm parameter")
> Reported-and-tested-by: syzbot+6ca9f7867b77c2d316ac@syzkaller.appspotmail.com
> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
> Tested-by: Oleksij Rempel <o.rempel@pengutronix.de>
> ---
> 
> Changes since RFT:
> 	- Added Tested-by: tag
> 
> ---
>  drivers/net/usb/asix.h         |  4 ++--
>  drivers/net/usb/asix_common.c  | 19 +++++++++++++------
>  drivers/net/usb/asix_devices.c | 21 ++++++++++++++++++---
>  3 files changed, 33 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/usb/asix.h b/drivers/net/usb/asix.h
> index 2a1e31def..4334aafab 100644
> --- a/drivers/net/usb/asix.h
> +++ b/drivers/net/usb/asix.h
> @@ -192,8 +192,8 @@ extern const struct driver_info ax88172a_info;
>  /* ASIX specific flags */
>  #define FLAG_EEPROM_MAC		(1UL << 0)  /* init device MAC from eeprom */
>  
> -int asix_read_cmd(struct usbnet *dev, u8 cmd, u16 value, u16 index,
> -		  u16 size, void *data, int in_pm);
> +int __must_check asix_read_cmd(struct usbnet *dev, u8 cmd, u16 value, u16 index,
> +			       u16 size, void *data, int in_pm);
>  
>  int asix_write_cmd(struct usbnet *dev, u8 cmd, u16 value, u16 index,
>  		   u16 size, void *data, int in_pm);
> diff --git a/drivers/net/usb/asix_common.c b/drivers/net/usb/asix_common.c
> index 71682970b..524805285 100644
> --- a/drivers/net/usb/asix_common.c
> +++ b/drivers/net/usb/asix_common.c
> @@ -11,8 +11,8 @@
>  
>  #define AX_HOST_EN_RETRIES	30
>  
> -int asix_read_cmd(struct usbnet *dev, u8 cmd, u16 value, u16 index,
> -		  u16 size, void *data, int in_pm)
> +int __must_check asix_read_cmd(struct usbnet *dev, u8 cmd, u16 value, u16 index,
> +			       u16 size, void *data, int in_pm)
>  {
>  	int ret;
>  	int (*fn)(struct usbnet *, u8, u8, u16, u16, void *, u16);
> @@ -27,9 +27,12 @@ int asix_read_cmd(struct usbnet *dev, u8 cmd, u16 value, u16 index,
>  	ret = fn(dev, cmd, USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
>  		 value, index, data, size);
>  
> -	if (unlikely(ret < 0))
> +	if (unlikely(ret < size)) {
> +		ret = ret < 0 ? ret : -ENODATA;
> +

Didn't I suggest using the proper USB core functions for this instead of
rolling your own functions?  We now have usb_control_msg_read() and
usb_control_msg_send() that prevents this type of thing from happening.

Ah, it's a bit more tangled up than that it seems, the number of layers
of abstractions here is odd and deep.  This change looks fine for now to
keep syzbot happy:

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>