Re: [PATCH] block: reexpand iov_iter after read/write

[Pavel Begunkov <asml.silence@gmail.com>]

On 01/04/2021 08:18, yangerkun wrote:
> 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.

Looks right,

Acked-by: Pavel Begunkov <asml.silencec@gmail.com>

> 
> blkdev_write_iter can trigger the problem too.
> 
> Signed-off-by: yangerkun <yangerkun@huawei.com>
> ---
>  fs/block_dev.c | 20 +++++++++++++++++---
>  1 file changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 92ed7d5df677..788e1014576f 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1680,6 +1680,7 @@ ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  	struct inode *bd_inode = bdev_file_inode(file);
>  	loff_t size = i_size_read(bd_inode);
>  	struct blk_plug plug;
> +	size_t shorted = 0;
>  	ssize_t ret;
>  
>  	if (bdev_read_only(I_BDEV(bd_inode)))
> @@ -1697,12 +1698,17 @@ ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  	if ((iocb->ki_flags & (IOCB_NOWAIT | IOCB_DIRECT)) == IOCB_NOWAIT)
>  		return -EOPNOTSUPP;
>  
> -	iov_iter_truncate(from, size - iocb->ki_pos);
> +	size -= iocb->ki_pos;
> +	if (iov_iter_count(from) > size) {
> +		shorted = iov_iter_count(from) - size;
> +		iov_iter_truncate(from, size);
> +	}
>  
>  	blk_start_plug(&plug);
>  	ret = __generic_file_write_iter(iocb, from);
>  	if (ret > 0)
>  		ret = generic_write_sync(iocb, ret);
> +	iov_iter_reexpand(from, iov_iter_count(from) + shorted);
>  	blk_finish_plug(&plug);
>  	return ret;
>  }
> @@ -1714,13 +1720,21 @@ ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
>  	struct inode *bd_inode = bdev_file_inode(file);
>  	loff_t size = i_size_read(bd_inode);
>  	loff_t pos = iocb->ki_pos;
> +	size_t shorted = 0;
> +	ssize_t ret;
>  
>  	if (pos >= size)
>  		return 0;
>  
>  	size -= pos;
> -	iov_iter_truncate(to, size);
> -	return generic_file_read_iter(iocb, to);
> +	if (iov_iter_count(to) > size) {
> +		shorted = iov_iter_count(to) - size;
> +		iov_iter_truncate(to, size);
> +	}
> +
> +	ret = generic_file_read_iter(iocb, to);
> +	iov_iter_reexpand(to, iov_iter_count(to) + shorted);
> +	return ret;
>  }
>  EXPORT_SYMBOL_GPL(blkdev_read_iter);
>  
> 

-- 
Pavel Begunkov