On Tue, May 06, 2025 at 01:55:54PM +0200, Christian Brauner wrote:
> Now that we have pidfs_{get,register}_pid() that needs to be paired with
> pidfs_put_pid() it's possible that someone pairs them with put_pid().
> Thus freeing struct pid while it's still used by pidfs. Notice when that
> happens. I'll also add a scheme to detect invalid uses of
> pidfs_get_pid() and pidfs_put_pid() later.
>
> Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
> ---
> kernel/pid.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/pid.c b/kernel/pid.c
> index 26f1e136f017..8317bcbc7cf7 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -100,6 +100,7 @@ void put_pid(struct pid *pid)
>
> ns = pid->numbers[pid->level].ns;
> if (refcount_dec_and_test(&pid->count)) {
> + WARN_ON_ONCE(pid->stashed);
> kmem_cache_free(ns->pid_cachep, pid);
> put_pid_ns(ns);
> }
> --
> 2.47.2
>
With the patch as proposed you are only catching the misuse if this is
the last ref though.
iow, the check should be hoisted above unrefing?
