ublk: validate physical_bs_shift, io_min_shift and io_opt_shift

ublk: validate physical_bs_shift, io_min_shift and io_opt_shift

ublk_validate_params() checks logical_bs_shift is within
[9, PAGE_SHIFT] but has no upper bound for physical_bs_shift,
io_min_shift, or io_opt_shift. A malicious userspace can set any
of these to a large value (e.g., 44), causing undefined behavior
from `1 << shift` in ublk_ctrl_start_dev() since the result is
stored in 32-bit unsigned int.

Cap all three at ilog2(SZ_256M) (28). 256M is big enough to cover
all practical block sizes, and originates from the maximum physical
block size possible in NVMe (lba_size * (1 + npwg), where npwg is
16-bit).

Also zero out ub->params with memset() when copy_from_user() fails
or ublk_validate_params() returns error, so that no stale or partial
params survive for a subsequent START_DEV to consume.

Fixes: 71f28f3136af ("ublk_drv: add io_uring based userspace block driver")
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Link: https://patch.msgid.link/20260506082238.22363-1-tom.leiming@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>