Oliver Neukum <oneukum@xxxxxxxx> writes:
> Hi,
>
> going through the USB network drivers looking for ways
> a malicious device could do us harm I found drivers taking
> the alignment coming from the device for granted.
>
> An example can be seen in qmi_wwan:
>
> while (offset + qmimux_hdr_sz < skb->len) {
> hdr = (struct qmimux_hdr*)(skb->data + offset);
> len = be16_to_cpu(hdr->pkt_len);
>
> As you can see the driver accesses stuff coming from the device with the
> expectation
> that it keep to natural alignment. On some architectures that is a way a
> device could use to do bad things to a host. What is to be done about
> that?
We can deal with this the same way we deal with hostile hot-plugged CPUs
or memory modules.
Yes, the aligment should probably be verified. But there are so many
ways a hostile network adapter can mess with us than I don't buy the
"malicious device" argument...
FWIW, the more recent rmnet demuxing implementation from Qualcomm seems
to suffer from the same problem.
struct sk_buff *rmnet_map_deaggregate(struct sk_buff *skb,
struct rmnet_port *port)
{
struct rmnet_map_header *maph;
struct sk_buff *skbn;
u32 packet_len;
if (skb->len == 0)
return NULL;
maph = (struct rmnet_map_header *)skb->data;
packet_len = ntohs(maph->pkt_len) + sizeof(struct rmnet_map_header);
(this implementation moves skb->data by packet_len instead of doing the
offset calculation, but I don't think that makes any difference?)
I guess there is no alignment guarantee here, whether the device is
malicious or not. So we probably have to deal with unaligned accesses to
maph/hdr->pkt_len?
Bjørn
