ublk: use unchecked copy helpers for bio page data

ublk: use unchecked copy helpers for bio page data

Bio pages may originate from slab caches that lack a usercopy region
(e.g. jbd2 frozen metadata buffers allocated via jbd2_alloc()).
When CONFIG_HARDENED_USERCOPY is enabled, copy_to_iter() calls
check_copy_size() which rejects these slab pages, triggering a
kernel BUG in usercopy_abort().

This is a false positive: the data is ordinary block I/O content —
the same data the loop driver writes to its backing file via
vfs_iter_write().  The bvec length is always trusted, so the size
check in check_copy_size() is not needed either.

Switch to _copy_to_iter()/_copy_from_iter() which skip the
check_copy_size() wrapper while the underlying copy_to_user()
remains unchanged.

Acked-by: Caleb Sander Mateos <csander@purestorage.com>
Fixes: 2299ceec364e ("ublk: use copy_{to,from}_iter() for user copy")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://patch.msgid.link/20260415230246.808176-1-tom.leiming@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>