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

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

On 09/04/2021 15:49, Pavel Begunkov wrote:
> 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:
...
>>  __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
...
>>
>> 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>

Fwiw, we need to forget to drag it through 5.13 + stable


>>
>> 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