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

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

On 4/28/21 7:16 AM, yangerkun wrote:
> Hi,
> 
> Should we pick this patch for 5.13?

Looks ok to me

> 
> 在 2021/4/16 1:39, Pavel Begunkov 写道:
>> On 15/04/2021 18:37, Pavel Begunkov wrote:
>>> 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
>>
>> Err, yypo, to _not_ forget to 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