NFSD: prevent integer overflow on 32 bit systems

stable inclusion
from stable-4.19.238
commit 3a2789e8ccb4a3e2a631f6817a2d3bb98b8c4fd8
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5A6BA


CVE: NA

--------------------------------

commit 23a9dbbe upstream.

On a 32 bit system, the "len * sizeof(*p)" operation can have an
integer overflow.

Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>