linux-kernel - Re: [PATCH v4 1/5] fuse: Fix leak in fuse_dentry

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Message-ID: <CAJfpegvFUasy_8djyvo-fpyboOLGwRV9k_CL-e1nqxcXHkvzOg@mail.gmail.com>
Date:   Fri, 21 May 2021 09:54:19 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Greg Kurz <groug@...d.org>,
        virtualization@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        virtio-fs-list <virtio-fs@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Max Reitz <mreitz@...hat.com>, Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH v4 1/5] fuse: Fix leak in fuse_dentry_automount() error path

On Thu, 20 May 2021 at 21:45, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Thu, May 20, 2021 at 05:46:50PM +0200, Greg Kurz wrote:
> > Some rollback was forgotten during the addition of crossmounts.
>
> Have you actually tested that?  Because I strongly suspect that
> by that point the ownership of fc and fm is with sb and those
> should be taken care of by deactivate_locked_super().

Not quite.  Patch looks correct because destruction of fm is done in
fuse_put_super(), which only gets called if the sb initialization gets
as far as setting up sb->s_root, which only happens after the
successful fuse_fill_super_submount() call in this case.

Doing the destruction from the various ->kill_sb() instances instead
of from ->put_super() would also fix this, but I'm not quite sure that
that would be any cleaner.

Thanks,
Miklos