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SubjectRe: [PATCH] once: Fix panic when module unload
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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@huawei.com/
>
> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: Eric Dumazet <edumazet@google.com>
> Reported-by: Minmin chen <chenmingmin@huawei.com>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
> 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);
> }
>

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