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 12:11:23 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     ChenXiaoSong <chenxiaosong2@...wei.com>
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

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