block: reexpand iov_iter after read/write

block: reexpand iov_iter after read/write

We get a bug:

BUG: KASAN: slab-out-of-bounds in iov_iter_revert+0x11c/0x404
lib/iov_iter.c:1139
Read of size 8 at addr ffff0000d3fb11f8 by task

CPU: 0 PID: 12582 Comm: syz-executor.2 Not tainted
5.10.0-00843-g352c8610ccd2 #2
Hardware name: linux,dummy-virt (DT)
Call trace:
 dump_backtrace+0x0/0x2d0 arch/arm64/kernel/stacktrace.c:132
 show_stack+0x28/0x34 arch/arm64/kernel/stacktrace.c:196
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x110/0x164 lib/dump_stack.c:118
 print_address_description+0x78/0x5c8 mm/kasan/report.c:385
 __kasan_report mm/kasan/report.c:545 [inline]
 kasan_report+0x148/0x1e4 mm/kasan/report.c:562
 check_memory_region_inline mm/kasan/generic.c:183 [inline]
 __asan_load8+0xb4/0xbc mm/kasan/generic.c:252
 iov_iter_revert+0x11c/0x404 lib/iov_iter.c:1139
 io_read fs/io_uring.c:3421 [inline]
 io_issue_sqe+0x2344/0x2d64 fs/io_uring.c:5943
 __io_queue_sqe+0x19c/0x520 fs/io_uring.c:6260
 io_queue_sqe+0x2a4/0x590 fs/io_uring.c:6326
 io_submit_sqe fs/io_uring.c:6395 [inline]
 io_submit_sqes+0x4c0/0xa04 fs/io_uring.c:6624
 __do_sys_io_uring_enter fs/io_uring.c:9013 [inline]
 __se_sys_io_uring_enter fs/io_uring.c:8960 [inline]
 __arm64_sys_io_uring_enter+0x190/0x708 fs/io_uring.c:8960
 __invoke_syscall arch/arm64/kernel/syscall.c:36 [inline]
 invoke_syscall arch/arm64/kernel/syscall.c:48 [inline]
 el0_svc_common arch/arm64/kernel/syscall.c:158 [inline]
 do_el0_svc+0x120/0x290 arch/arm64/kernel/syscall.c:227
 el0_svc+0x1c/0x28 arch/arm64/kernel/entry-common.c:367
 el0_sync_handler+0x98/0x170 arch/arm64/kernel/entry-common.c:383
 el0_sync+0x140/0x180 arch/arm64/kernel/entry.S:670

Allocated by task 12570:
 stack_trace_save+0x80/0xb8 kernel/stacktrace.c:121
 kasan_save_stack mm/kasan/common.c:48 [inline]
 kasan_set_track mm/kasan/common.c:56 [inline]
 __kasan_kmalloc+0xdc/0x120 mm/kasan/common.c:461
 kasan_kmalloc+0xc/0x14 mm/kasan/common.c:475
 __kmalloc+0x23c/0x334 mm/slub.c:3970
 kmalloc include/linux/slab.h:557 [inline]
 __io_alloc_async_data+0x68/0x9c fs/io_uring.c:3210
 io_setup_async_rw fs/io_uring.c:3229 [inline]
 io_read fs/io_uring.c:3436 [inline]
 io_issue_sqe+0x2954/0x2d64 fs/io_uring.c:5943
 __io_queue_sqe+0x19c/0x520 fs/io_uring.c:6260
 io_queue_sqe+0x2a4/0x590 fs/io_uring.c:6326
 io_submit_sqe fs/io_uring.c:6395 [inline]
 io_submit_sqes+0x4c0/0xa04 fs/io_uring.c:6624
 __do_sys_io_uring_enter fs/io_uring.c:9013 [inline]
 __se_sys_io_uring_enter fs/io_uring.c:8960 [inline]
 __arm64_sys_io_uring_enter+0x190/0x708 fs/io_uring.c:8960
 __invoke_syscall arch/arm64/kernel/syscall.c:36 [inline]
 invoke_syscall arch/arm64/kernel/syscall.c:48 [inline]
 el0_svc_common arch/arm64/kernel/syscall.c:158 [inline]
 do_el0_svc+0x120/0x290 arch/arm64/kernel/syscall.c:227
 el0_svc+0x1c/0x28 arch/arm64/kernel/entry-common.c:367
 el0_sync_handler+0x98/0x170 arch/arm64/kernel/entry-common.c:383
 el0_sync+0x140/0x180 arch/arm64/kernel/entry.S:670

Freed by task 12570:
 stack_trace_save+0x80/0xb8 kernel/stacktrace.c:121
 kasan_save_stack mm/kasan/common.c:48 [inline]
 kasan_set_track+0x38/0x6c mm/kasan/common.c:56
 kasan_set_free_info+0x20/0x40 mm/kasan/generic.c:355
 __kasan_slab_free+0x124/0x150 mm/kasan/common.c:422
 kasan_slab_free+0x10/0x1c mm/kasan/common.c:431
 slab_free_hook mm/slub.c:1544 [inline]
 slab_free_freelist_hook mm/slub.c:1577 [inline]
 slab_free mm/slub.c:3142 [inline]
 kfree+0x104/0x38c mm/slub.c:4124
 io_dismantle_req fs/io_uring.c:1855 [inline]
 __io_free_req+0x70/0x254 fs/io_uring.c:1867
 io_put_req_find_next fs/io_uring.c:2173 [inline]
 __io_queue_sqe+0x1fc/0x520 fs/io_uring.c:6279
 __io_req_task_submit+0x154/0x21c fs/io_uring.c:2051
 io_req_task_submit+0x2c/0x44 fs/io_uring.c:2063
 task_work_run+0xdc/0x128 kernel/task_work.c:151
 get_signal+0x6f8/0x980 kernel/signal.c:2562
 do_signal+0x108/0x3a4 arch/arm64/kernel/signal.c:658
 do_notify_resume+0xbc/0x25c arch/arm64/kernel/signal.c:722
 work_pending+0xc/0x180

blkdev_read_iter can truncate iov_iter's count since the count + pos may
exceed the size of the blkdev. This will confuse io_read that we have
consume the iovec. And once we do the iov_iter_revert in io_read, we
will trigger the slab-out-of-bounds. Fix it by reexpand the count with
size has been truncated.

blkdev_write_iter can trigger the problem too.

Signed-off-by: yangerkun <yangerkun@huawei.com>
Acked-by: Pavel Begunkov <asml.silencec@gmail.com>
Link: https://lore.kernel.org/r/20210401071807.3328235-1-yangerkun@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>