tcp: fix skb_copy_ubufs() vs BIG TCP

tcp: fix skb_copy_ubufs() vs BIG TCP

David Ahern reported crashes in skb_copy_ubufs() caused by TCP tx zerocopy
using hugepages, and skb length bigger than ~68 KB.

skb_copy_ubufs() assumed it could copy all payload using up to
MAX_SKB_FRAGS order-0 pages.

This assumption broke when BIG TCP was able to put up to 512 KB per skb.

We did not hit this bug at Google because we use CONFIG_MAX_SKB_FRAGS=45
and limit gso_max_size to 180000.

A solution is to use higher order pages if needed.

v2: add missing __GFP_COMP, or we leak memory.

Fixes: 7c4e983c4f3c ("net: allow gso_max_size to exceed 65536")
Reported-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/netdev/c70000f6-baa4-4a05-46d0-4b3e0dc1ccc8@gmail.com/T/
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Xin Long <lucien.xin@gmail.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Coco Li <lixiaoyan@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>