sctp: Make sure N * sizeof(union sctp_addr) does not overflow (CVE-2008-2826)

sctp: Make sure N * sizeof(union sctp_addr) does not overflow (CVE-2008-2826)

[backport of 2.6 commit 735ce972fbc8a65fb17788debd7bbe7b4383cc62]

As noticed by Gabriel Campana, the kmalloc() length arg
passed in by sctp_getsockopt_local_addrs_old() can overflow
if ->addr_num is large enough.

Therefore, enforce an appropriate limit.

Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>