AIO: properly check iovec sizes

In Linus's tree, the iovec code has been reworked massively, but in
older kernels the AIO layer should be checking this before passing the
request on to other layers.

Many thanks to Ben Hawkes of Google Project Zero for pointing out the
issue.

Change-Id: I625e1b4376bb2342d6c5f88eb3f202e99a0c5b07
Reported-by: Ben Hawkes <hawkes@google.com>
Acked-by: Benjamin LaHaise <bcrl@kvack.org>
Tested-by: Willy Tarreau <w@1wt.eu>
[backported to 3.10 - willy]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Git-commit: 8a5e5e02fc83aaf67053ab53b359af08c6c49aaf
Git-repo: https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git


Signed-off-by: Ravi Kumar Siddojigari <rsiddoji@codeaurora.org>