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

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Message-ID: <209361bb-9e15-ebaf-2ff8-5846d5bfbbc2@huawei.com>
Date:   Tue, 26 Oct 2021 10:18:11 +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 2021/10/20 20:30, Greg KH 写道:
> On Wed, Oct 13, 2021 at 06:49:06PM +0800, chenxiaosong (A) wrote:
>> 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?
> 
> That would be a better idea, but still, this is not obvious that this is
> the correct fix at all...
> .
> 
Why is this patch not correct? Can you tell me more about it? Thanks.