net: sock: validate data_len before allocating skb in sock_alloc_send_pskb()

net: sock: validate data_len before allocating skb in sock_alloc_send_pskb()

Bugdb: 13966
We need to validate the number of pages consumed by data_len, otherwise frags
array could be overflowed by userspace. So this patch validate data_len and
return -EMSGSIZE when data_len may occupies more frags than MAX_SKB_FRAGS.
This fixes: CVE-2012-2136
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>