rds: signedness bug

rds: signedness bug

In the original code if the copy_from_user() fails in rds_rdma_pages()
then the error handling fails and we get a stack trace from kmalloc().

<amended commit message by hbugge>

This bug was originally fixed in v2.6.36-rc5. However, commit
edc31ebe9e36 ("[patch1/3] Merge for Mellanox OFED R2, 0080 release")
re-introduces the bug, most probably because the Mellanox OFED didn't
have the upstream fix.

So, this bug has been present since v2.6.39-400.9.0 and is present in
all our releases from uek2 to uek5.

</amended>

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 9b9d2e00bfa592aceda7b43da76c670df61faa97)

Orabug: 28319166

Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com>
Fixes: edc31ebe9e36d87dcd08931784a49c2e75eed359
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>