linux-ext4 - Re: [PATCH] ext4: do not use extent after put

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Message-ID: <a77ce068-aa0f-77f3-abc4-58c0224757b0@huawei.com>
Date:   Fri, 30 Oct 2020 09:23:38 +0800
From:   yangerkun <yangerkun@...wei.com>
To:     Ritesh Harjani <riteshh@...ux.ibm.com>, <adilger@...ger.ca>
CC:     <tytso@....edu>, <jack@...e.com>, <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: do not use extent after put_bh



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
> .