[CVE-2017-7895][T/Y SRU] Fix for CVE-2017-7895

[Po-Hsu Lin]

For Yakkety, the fix (13bf9fbf) requires another cherry-pick (db44bac4)
to tidy up the struct access first. As the patch is just make it easier
to access the variable, the possible impact should be minimum.

For Trusty, it will need two more patches in advance. Including one
cherry-pick (d40aa337) to move assignments out of an if conditional,
a backport (6625d091) to take only the change for fs/nfsd/nfs3xdr.c
to ensures the total length of the incoming NFS WRITE request. And
then followed by those two cherry-picks for Yakkety.

This CVE was mark as needed for T/Y.

[Regression Potential]
The only possible impact is to the RDMA transport, since the backport
does not include the change to fix its read logic in
/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c

However, the aforementioned read logic belongs to the XDR round-up logic,
which has not landed in Trusty at all (fcbeced5), thus the impact should
be minimum.


-- 
1.7.9.5