When we copy 32bit ->msg_control contents to kernel, we walk the same
userland data twice without sanity checks on the second pass.

Second version of this patch: the original broke with 64-bit arches
running 32-bit-compat-mode executables doing sendmsg() syscalls with
unaligned CMSG data areas

Another thing is that we use kmalloc() to allocate and sock_kfree_s()
to free afterwards; less serious, but also needs fixing.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NDavid Woodhouse <dwmw2@infradead.org>
Signed-off-by: NChris Wright <chrisw@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>