Re: [PATCH] ext4: do not use extent after put_bh

[yangerkun <yangerkun@huawei.com>]

在 2020/10/30 0:08, Ritesh Harjani 写道:
> 
> 
> On 10/28/20 11:26 AM, yangerkun wrote:
>> ext4_ext_search_right will read more extent block and call put_bh after
>> we get the information we need. However ret_ex will break this and may
>> cause use-after-free once pagecache has been freed. Fix it by dup the
>> extent we need.
> 
> 
> It would be good if we have a test case to reproduce it. Do you?
> Ideally it should go in fstests, if you have some way to forcefully
> reproduce it/simulate it. Let me know, if needed, I can as well help to
> get those into fstests.

Sorry for that. I found this bug while reading source code. Not with a 
testcase.

And time leave for drop pagecache is so small(time between 
get_implied_cluster_alloc and ext4_ext_search_right in 
ext4_ext_map_blocks, other caller for ext4_ext_search_right won't use 
@ret_ex). It may difficult to reproduce it expect a delay injection.

Thanks,
Kun.

> 
> -ritesh
> .