Re: OOB accesses in ax88179_rx_fixup() (in USB network card driver) - variants

[Marcin Kozlowski <marcinguy@xxxxxxxxx>]

gl620a.c is some usb to usb computer cable, and lg-vl600.c a usb 4g dongle. Both drivers seem NOT to use skb metadata (they take packet len and count from skb->data directly).

Why would ASIX driver use metadata and others (those 2) don't? 

Could not find any info on skb Metadata.

Thanks, 

Marcin

On Mon, 21 Mar 2022, 10:39 Marcin Kozlowski <marcinguy@xxxxxxxxx> wrote:

Hi List,

Don't have much experience and knowledge in that area.

Found this:

https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git/commit/?h=usb-linus&id=57bc3d3ae8c14df3ceb4e17d26ddf9eeab304581

Checked out a few drivers code and wondered if anybody did a variant analysis of this (possibly yes?) However, it seems like Kernel drivers code for gl620a.c and lg-vl600.c (quick search) don't "Make sure that the bounds of the metadata array are inside the SKB (and in front of the counter at the end)."

Example from gl620a.c

https://github.com/torvalds/linux/blob/master/drivers/net/usb/gl620a.c

I think, there is no check for:

/* Make sure that the bounds of the metadata array are inside the SKB
* (and in front of the counter at the end).
*/
if (pkt_cnt * 2 + hdr_off > skb->len)
return 0;

Most likely false positive. Would be great to verify this and learn about it.

Thanks,

Marcin