splice: Apply generic position and size checks to each write

commit 894c6350eaad7e613ae267504014a456e00a3e2a from the 3.2-stable branch.

We need to check the position and size of file writes against various
limits, using generic_write_check().  This was not being done for
the splice write path.  It was fixed upstream by commit 8d0207652cbe
("->splice_write() via ->write_iter()") but we can't apply that.

CVE-2014-7822

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
[Ben fixed it in 3.2 stable, i ported it to 3.10 stable]
Signed-off-by: Zhang Zhen <zhenzhang.zhang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>