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

[chenxiaosong (A)]

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@xxxxxxxxxx/
> > > > >
> > > > >
> > > > > Fixes: 79c0b2df79eb (add filesystem subtype support)
> > > > > Cc: David Howells <dhowells@xxxxxxxxxx>
> > > > > Signed-off-by: ChenXiaoSong <chenxiaosong2@xxxxxxxxxx>
> > > > > ---
> > > > > 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.