Re: [PATCH] once: Fix panic when module unload

[Kefeng Wang]

Hi all, kindly ping...

On 2021/6/22 10:21, Kefeng Wang wrote:
> DO_ONCE
> DEFINE_STATIC_KEY_TRUE(___once_key);
> __do_once_done
>    once_disable_jump(once_key);
>      INIT_WORK(&w->work, once_deferred);
>      struct once_work *w;
>      w->key = key;
>      schedule_work(&w->work);                     module unload
>                                                     //*the key is destroy*
> process_one_work
>    once_deferred
>      BUG_ON(!static_key_enabled(work->key));
>         static_key_count((struct static_key *)x)    //*access key, crash*
>
> When module uses DO_ONCE mechanism, it could crash due to the above
> concurrency problem, we could reproduce it with link[1].
>
> Fix it by add/put module refcount in the once work process.
>
> [1]
> https://lore.kernel.org/netdev/eaa6c371-465e-57eb-6be9-f4b16b9d7cbf@xxxxxxxxxx/
>
> Cc: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> Reported-by: Minmin chen <chenmingmin@xxxxxxxxxx>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> ---
>   lib/once.c | 17 +++++++++++++++++
>   1 file changed, 17 insertions(+)
>
> diff --git a/lib/once.c b/lib/once.c
> index 8b7d6235217e..959f8db41ccf 100644
> --- a/lib/once.c
> +++ b/lib/once.c
> @@ -3,10 +3,12 @@
>   #include <linux/spinlock.h>
>   #include <linux/once.h>
>   #include <linux/random.h>
> +#include <linux/module.h>
>   
>   struct once_work {
>   	struct work_struct work;
>   	struct static_key_true *key;
> +	struct module *module;
>   };
>   
>   static void once_deferred(struct work_struct *w)
> @@ -16,11 +18,24 @@ static void once_deferred(struct work_struct *w)
>   	work = container_of(w, struct once_work, work);
>   	BUG_ON(!static_key_enabled(work->key));
>   	static_branch_disable(work->key);
> +	module_put(work->module);
>   	kfree(work);
>   }
>   
> +static struct module *find_module_by_key(struct static_key_true *key)
> +{
> +	struct module *mod;
> +
> +	preempt_disable();
> +	mod = __module_address((unsigned long)key);
> +	preempt_enable();
> +
> +	return mod;
> +}
> +
>   static void once_disable_jump(struct static_key_true *key)
>   {
> +	struct module *mod = find_module_by_key(key);
>   	struct once_work *w;
>   
>   	w = kmalloc(sizeof(*w), GFP_ATOMIC);
> @@ -29,6 +44,8 @@ static void once_disable_jump(struct static_key_true *key)
>   
>   	INIT_WORK(&w->work, once_deferred);
>   	w->key = key;
> +	w->module = mod;
> +	__module_get(mod);
>   	schedule_work(&w->work);
>   }
>