From: Krzysztof Kozlowski <krzk@kernel.org>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Aditya Pakki <pakki001@umn.edu>,
Stefan Hajnoczi <stefanha@redhat.com>,
Miklos Szeredi <miklos@szeredi.hu>,
virtualization@lists.linux-foundation.org,
linux-fsdevel@vger.kernel.org,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] fuse: Avoid potential use after free
Date: Wed, 21 Apr 2021 15:28:01 +0200 [thread overview]
Message-ID: <CAJKOXPc-GuTmVzWPXWqSegtckDsfyYj_aOKwK1TKCsYFkK681A@mail.gmail.com> (raw)
In-Reply-To: <20210407155031.GA1014852@redhat.com>
On Wed, 7 Apr 2021 at 23:25, Vivek Goyal <vgoyal@redhat.com> wrote:
>
> On Tue, Apr 06, 2021 at 06:53:32PM -0500, Aditya Pakki wrote:
> > In virtio_fs_get_tree, after fm is freed, it is again freed in case
> > s_root is NULL and virtio_fs_fill_super() returns an error. To avoid
> > a double free, set fm to NULL.
> >
> > Signed-off-by: Aditya Pakki <pakki001@umn.edu>
> > ---
> > fs/fuse/virtio_fs.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
> > index 4ee6f734ba83..a7484c1539bf 100644
> > --- a/fs/fuse/virtio_fs.c
> > +++ b/fs/fuse/virtio_fs.c
> > @@ -1447,6 +1447,7 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
> > if (fsc->s_fs_info) {
> > fuse_conn_put(fc);
> > kfree(fm);
> > + fm = NULL;
>
> I think both the code paths are mutually exclusive and that's why we
> don't double free it.
>
> sget_fc(), can either return existing super block which is already
> initialized, or it can create a new super block which need to
> initialize further.
>
> If if get an existing super block, in that case fs->s_fs_info will
> still be set and we need to free fm (as we did not use it). But in
> that case this super block is already initialized so sb->s_root
> should be non-null and we will not call virtio_fs_fill_super()
> on this. And hence we will not get into kfree(fm) again.
>
> Same applies to fuse_conn_put(fc) call as well.
>
> So I think this patch is not needed. I think sget_fc() semantics are
> not obvious and that confuses the reader of the code.
This patch might be harmful, might be not. Probably should be skipped
due to uncertain intentions:
https://lore.kernel.org/linux-nfs/YH+7ZydHv4+Y1hlx@kroah.com/
Best regards,
Krzysztof
next prev parent reply other threads:[~2021-04-21 13:28 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-06 23:53 [PATCH] fuse: Avoid potential use after free Aditya Pakki
2021-04-07 15:50 ` Vivek Goyal
2021-04-21 13:28 ` Krzysztof Kozlowski [this message]
2021-04-22 0:44 ` Al Viro
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