sctp: prevent reading out-of-bounds memory

Two user-controlled allocations in SCTP are subsequently dereferenced as
sockaddr structs, without checking if the dereferenced struct members fall
beyond the end of the allocated chunk.  There doesn't appear to be any
information leakage here based on how these members are used and
additional checking, but it's still worth fixing.

[akpm@linux-foundation.org: remove unfashionable newlines, fix gmail tab->space conversion]
Signed-off-by: Dan Rosenberg <dan.j.rosenberg@gmail.com>
Acked-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>