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 18:38:12 +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 18:11, 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.