Re: [PATCH] mm: kfence: fix using kfence_metadata without initialization in show_object()

[Marco Elver <elver@google.com>]

On Wed, 15 Mar 2023 at 04:45, Muchun Song <songmuchun@bytedance.com> wrote:
>
> The variable kfence_metadata is initialized in kfence_init_pool(), then, it is
> not initialized if kfence is disabled after booting. In this case, kfence_metadata
> will be used (e.g. ->lock and ->state fields) without initialization when reading
> /sys/kernel/debug/kfence/objects. There will be a warning if you enable
> CONFIG_DEBUG_SPINLOCK. Fix it by creating debugfs files when necessary.
>
> Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure")
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

Tested-by: Marco Elver <elver@google.com>
Reviewed-by: Marco Elver <elver@google.com>

Good catch!

> ---
>  mm/kfence/core.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index 5349c37a5dac..79c94ee55f97 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -726,10 +726,14 @@ static const struct seq_operations objects_sops = {
>  };
>  DEFINE_SEQ_ATTRIBUTE(objects);
>
> -static int __init kfence_debugfs_init(void)
> +static int kfence_debugfs_init(void)
>  {
> -       struct dentry *kfence_dir = debugfs_create_dir("kfence", NULL);
> +       struct dentry *kfence_dir;
>
> +       if (!READ_ONCE(kfence_enabled))
> +               return 0;
> +
> +       kfence_dir = debugfs_create_dir("kfence", NULL);
>         debugfs_create_file("stats", 0444, kfence_dir, NULL, &stats_fops);
>         debugfs_create_file("objects", 0400, kfence_dir, NULL, &objects_fops);
>         return 0;
> @@ -883,6 +887,8 @@ static int kfence_init_late(void)
>         }
>
>         kfence_init_enable();
> +       kfence_debugfs_init();
> +
>         return 0;
>  }
>
> --
> 2.11.0
>