On Mon, Mar 22, 2021 at 10:18:31PM -0700, Lv Yunlong wrote:
> In virtio_fs_get_tree, fm is allocated by kzalloc() and
> assigned to fsc->s_fs_info by fsc->s_fs_info=fm statement.
> If the kzalloc() failed, it will goto err directly, so that
> fsc->s_fs_info must be non-NULL and fm will be freed.
sget_fc() will either consume fsc->s_fs_info in case a new super
block is allocated and set fsc->s_fs_info. In that case we don't
free fc or fm.
Or, sget_fc() will return with fsc->s_fs_info set in case we already
found a super block. In that case we need to free fc and fm.
In case of error from sget_fc(), fc/fm need to be freed first and
then error needs to be returned to caller.
if (IS_ERR(sb))
return PTR_ERR(sb);
If we allocated a new super block in sget_fc(), then next step is
to initialize it.
if (!sb->s_root) {
err = virtio_fs_fill_super(sb, fsc);
}
If we run into errors here, then fc/fm need to be freed.
So current code looks fine to me.
Vivek
>
> But later fm is freed again when virtio_fs_fill_super() fialed.
> I think the statement if (fsc->s_fs_info) {kfree(fm);} is
> misplaced.
>
> My patch puts this statement in the correct palce to avoid
> double free.
>
> Signed-off-by: Lv Yunlong <lyl2...@mail.ustc.edu.cn>
> ---
> fs/fuse/virtio_fs.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
> index 8868ac31a3c0..727cf436828f 100644
> --- a/fs/fuse/virtio_fs.c
> +++ b/fs/fuse/virtio_fs.c
> @@ -1437,10 +1437,7 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
>
> fsc->s_fs_info = fm;
> sb = sget_fc(fsc, virtio_fs_test_super, set_anon_super_fc);
> - if (fsc->s_fs_info) {
> - fuse_conn_put(fc);
> - kfree(fm);
> - }
> +
> if (IS_ERR(sb))
> return PTR_ERR(sb);
>
> @@ -1457,6 +1454,11 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
> sb->s_flags |= SB_ACTIVE;
> }
>
> + if (fsc->s_fs_info) {
> + fuse_conn_put(fc);
> + kfree(fm);
> + }
> +
> WARN_ON(fsc->root);
> fsc->root = dget(sb->s_root);
> return 0;
> --
> 2.25.1
>
>
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