2017-04-27, 11:21:51 +0200, Jason A. Donenfeld wrote:
> However, perhaps there's the chance that fraglist skbs having
> separate fraglists are actually forbidden? Is this the case?
Hmm, I think this can actually happen:
/* net/ipv4/ip_fragment.c */
static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
struct net_device *dev)
{
...
/* If the first fragment is fragmented itself, we split
* it to two chunks: the first with data and paged part
* and the second, holding only fragments. */
if (skb_has_frag_list(head)) {
struct sk_buff *clone;
int i, plen = 0;
clone = alloc_skb(0, GFP_ATOMIC);
if (!clone)
goto out_nomem;
clone->next = head->next;
head->next = clone;
skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
skb_frag_list_init(head);
for (i = 0; i < skb_shinfo(head)->nr_frags; i++)
plen += skb_frag_size(&skb_shinfo(head)->frags[i]);
clone->len = clone->data_len = head->data_len - plen;
head->data_len -= clone->len;
head->len -= clone->len;
clone->csum = 0;
clone->ip_summed = head->ip_summed;
add_frag_mem_limit(qp->q.net, clone->truesize);
}
...
}
You can test that with a vxlan tunnel on top of a vxlan tunnel ("real"
MTU is 1500, first tunnel MTU set to 10000, second tunnel MTU set to
40000 -- or anything, as long as they both get fragmented).
--
Sabrina
