On Wed, 2017-01-25 at 16:26 +, Paul Durrant wrote:
> Sowmini points out two vulnerabilities in xen-netfront:
>
> a) The code assumes that skb->len is at least ETH_HLEN.
> b) The code assumes that at least ETH_HLEN octets are in the linear
>port of the socket buffer.
>
> This patch adds tests for both of these, and in the case of the latter
> pulls sufficient bytes into the linear area.
>
> Signed-off-by: Paul Durrant
> Reported-by: Sowmini Varadhan
> Tested-by: Sowmini Varadhan
> ---
> Cc: Boris Ostrovsky
> Cc: Juergen Gross
> ---
> drivers/net/xen-netfront.c | 9 +
> 1 file changed, 9 insertions(+)
>
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index 40f26b6..0478809 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -567,6 +567,10 @@ static int xennet_start_xmit(struct sk_buff *skb, struct
> net_device *dev)
> u16 queue_index;
> struct sk_buff *nskb;
>
> + /* Basic sanity check */
> + if (unlikely(skb->len < ETH_HLEN))
> + goto drop;
> +
> /* Drop the packet if no queues are set up */
> if (num_queues < 1)
> goto drop;
> @@ -609,6 +613,11 @@ static int xennet_start_xmit(struct sk_buff *skb, struct
> net_device *dev)
> }
>
> len = skb_headlen(skb);
> + if (unlikely(len < ETH_HLEN)) {
> + if (!__pskb_pull_tail(skb, ETH_HLEN - len))
> + goto drop;
> + len = ETH_HLEN;
> + }
Looks like duplicated code, and buggy, considering the code above
page = virt_to_page(skb->data);
offset = offset_in_page(skb->data);
Your patch might end up with skb->data/head being reallocated, and use
after free would happen.
What about something like that ?
diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index
40f26b69beb11459f0566fc1d1d739aa75e643bf..99a67fe4de86d3141169143b0820d00968cb09f2
100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -583,6 +583,8 @@ static int xennet_start_xmit(struct sk_buff *skb, struct
net_device *dev)
skb->len);
goto drop;
}
+ if (!pskb_may_pull(skb, ETH_HLEN))
+ goto drop;
slots = xennet_count_skb_slots(skb);
if (unlikely(slots > MAX_XEN_SKB_FRAGS + 1)) {
___
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