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@xxxxxxxxx>
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@xxxxxxxxxx>
>> ---
>> 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
