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Re: [Xen-devel] [PATCH net-next v2 6/9] xen-netback: Handle guests with too many frags



On 16/12/13 18:09, Wei Liu wrote:
diff --git a/drivers/net/xen-netback/netback.c 
b/drivers/net/xen-netback/netback.c
index e26cdda..f6ed1c8 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -906,11 +906,15 @@ static struct gnttab_map_grant_ref 
*xenvif_get_requests(struct xenvif *vif,
        u16 pending_idx = *((u16 *)skb->data);
        int start;
        pending_ring_idx_t index;
-       unsigned int nr_slots;
+       unsigned int nr_slots, frag_overflow = 0;

        /* At this point shinfo->nr_frags is in fact the number of
         * slots, which can be as large as XEN_NETBK_LEGACY_SLOTS_MAX.
         */
+       if (shinfo->nr_frags > MAX_SKB_FRAGS) {
+               frag_overflow = shinfo->nr_frags - MAX_SKB_FRAGS;
+               shinfo->nr_frags = MAX_SKB_FRAGS;
+       }
        nr_slots = shinfo->nr_frags;


It is also probably better to check whether shinfo->nr_frags is too
large which makes frag_overflow > MAX_SKB_FRAGS. I know skb should be
already be valid at this point but it wouldn't hurt to be more careful.
Ok, I've added this:
        /* At this point shinfo->nr_frags is in fact the number of
         * slots, which can be as large as XEN_NETBK_LEGACY_SLOTS_MAX.
         */
+       if (shinfo->nr_frags > MAX_SKB_FRAGS) {
+               if (shinfo->nr_frags > XEN_NETBK_LEGACY_SLOTS_MAX) return NULL;
+               frag_overflow = shinfo->nr_frags - MAX_SKB_FRAGS;


What I suggested is

    BUG_ON(frag_overflow > MAX_SKB_FRAGS)

Ok, I've changed it.

Zoli


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