loop: loop_set_status_from_info() check before assignment

In the Linux kernel, the following vulnerability has been resolved:

loop: loop_set_status_from_info() check before assignment

In loop_set_status_from_info(), lo->lo_offset and lo->lo_sizelimit should

be checked before reassignment, because if an overflow error occurs, the

original correct value will be changed to the wrong value, and it will not

be changed back.

More, the original patch did not solve the problem, the value was set and

ioctl returned an error, but the subsequent io used the value in the loop

driver, which still caused an alarm:

loop_handle_cmd

do_req_filebacked

loff_t pos = ((loff_t) blk_rq_pos(rq) << 9) + lo->lo_offset;

lo_rw_aio

cmd->iocb.ki_pos = pos