linux-kernel - Re: [PATCH 4.19,v2] VFS: Fix fuseblk memory leak caused by mount concurrency

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Date:   Wed, 13 Oct 2021 18:49:06 +0800
From:   "chenxiaosong (A)" <chenxiaosong2@...wei.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     <viro@...iv.linux.org.uk>, <stable@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <dhowells@...hat.com>, <yukuai3@...wei.com>, <yi.zhang@...wei.com>,
        <zhangxiaoxu5@...wei.com>
Subject: Re: [PATCH 4.19,v2] VFS: Fix fuseblk memory leak caused by mount
 concurrency

在 2021/10/13 18:38, chenxiaosong (A) 写道:
> 在 2021/10/13 18:11, Greg KH 写道:
>> On Wed, Oct 13, 2021 at 05:51:01PM +0800, ChenXiaoSong wrote:
>>> If two processes mount same superblock, memory leak occurs:
>>>
>>> CPU0               |  CPU1
>>> do_new_mount       |  do_new_mount
>>>    fs_set_subtype   |    fs_set_subtype
>>>      kstrdup        |
>>>                     |      kstrdup
>>>      memrory leak   |
>>>
>>> Fix this by adding a write lock while calling fs_set_subtype.
>>>
>>> Linus's tree already have refactoring patchset [1], one of them can 
>>> fix this bug:
>>>          c30da2e981a7 (fuse: convert to use the new mount API)
>>>
>>> Since we did not merge the refactoring patchset in this branch, I 
>>> create this patch.
>>>
>>> [1] 
>>> https://patchwork.kernel.org/project/linux-fsdevel/patch/20190903113640.7984-3-mszeredi@redhat.com/ 
>>>
>>>
>>> Fixes: 79c0b2df79eb (add filesystem subtype support)
>>> Cc: David Howells <dhowells@...hat.com>
>>> Signed-off-by: ChenXiaoSong <chenxiaosong2@...wei.com>
>>> ---
>>> v1: Can not mount sshfs ([PATCH linux-4.19.y] VFS: Fix fuseblk memory 
>>> leak caused by mount concurrency)
>>> v2: Use write lock while writing superblock
>>>
>>>   fs/namespace.c | 9 ++++++---
>>>   1 file changed, 6 insertions(+), 3 deletions(-)
>>
>> As you are referring to a fuse-only patch above, why are you trying to
>> resolve this issue in the core namespace code instead?
>>
>> How does fuse have anything to do with this?
>>
>> confused,
>>
>> greg k-h
>> .
>>
> 
> Now, only `fuse_fs_type` and `fuseblk_fs_type` has `FS_HAS_SUBTYPE` flag 
> in kernel code, but maybe there is a filesystem module(`struct 
> file_system_type` has `FS_HAS_SUBTYPE` flag). And only mounting fuseblk 
> filesystem(e.g. ntfs) will occur memory leak now.

How about updating the subject as: VFS: Fix memory leak caused by 
mounting fs with subtype concurrency?