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

From: Miklos Szeredi <miklos@szeredi.hu>
To: Hangyu Hua <hbh25y@gmail.com>
Cc: vgoyal@redhat.com, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fs: fuse: dax: set fc->dax to NULL in fuse_dax_conn_free()
Date: Thu, 30 Nov 2023 11:54:39 +0100	[thread overview]
Message-ID: <CAJfpegvN5Rzy1_2v3oaf1Rp_LP_t3w6W_-Ozn1ADoCLGSKBk+Q@mail.gmail.com> (raw)
In-Reply-To: <20231116075726.28634-1-hbh25y@gmail.com>

On Thu, 16 Nov 2023 at 08:57, Hangyu Hua <hbh25y@gmail.com> 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@gmail.com>
> ---
>  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()?

Thanks,
Miklos

>         }
>  }
>
> --
> 2.34.1
>