Re: [PATCH] fs: fuse: dax: set fc->dax to NULL in fuse_dax_conn_free()

[Hangyu Hua]

On 30/11/2023 18:54, Miklos Szeredi wrote:
> On Thu, 16 Nov 2023 at 08:57, Hangyu Hua <hbh25y@xxxxxxxxx> wrote:
> > fuse_dax_conn_free() will be called when fuse_fill_super_common() fails
> > after fuse_dax_conn_alloc(). Then deactivate_locked_super() in
> > virtio_fs_get_tree() will call virtio_kill_sb() to release the discarded
> > superblock. This will call fuse_dax_conn_free() again in fuse_conn_put(),
> > resulting in a possible double free.
> >
> > Fixes: 1dd539577c42 ("virtiofs: add a mount option to enable dax")
> > Signed-off-by: Hangyu Hua <hbh25y@xxxxxxxxx>
> > ---
> >   fs/fuse/dax.c | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
> > index 23904a6a9a96..12ef91d170bb 100644
> > --- a/fs/fuse/dax.c
> > +++ b/fs/fuse/dax.c
> > @@ -1222,6 +1222,7 @@ void fuse_dax_conn_free(struct fuse_conn *fc)
> >          if (fc->dax) {
> >                  fuse_free_dax_mem_ranges(&fc->dax->free_ranges);
> >                  kfree(fc->dax);
> > +               fc->dax = NULL;
>
> Is there a reason not to simply remove the fuse_dax_conn_free() call
> from the cleanup path in fuse_fill_super_common()?

I think setting fc->dax to NULL keeps the memory allocation and release 
functions together in fuse_fill_super_common more readable. What do you 
think?

Thanks,
Hangyu

> Thanks,
> Miklos
>
>
> >          }
> >   }
> >
> > --
> > 2.34.1