Re: [PATCH v2] RDMA/rtrs: Fix use-after-free in path files cleanup

[Leon Romanovsky <leon@kernel.org>]

On Mon, May 11, 2026 at 09:08:04PM +0800, Guangshuo Li wrote:
> Once kobject_put() is called on srv_path->kobj, the release callback may be
> triggered and srv_path may be freed. Therefore, srv_path must not be used
> after kobject_put(&srv_path->kobj).
> 
> Both rtrs_srv_create_path_files() and rtrs_srv_destroy_path_files()
> currently call rtrs_srv_destroy_once_sysfs_root_folders(srv_path) after
> kobject_put(&srv_path->kobj). Although the call site only passes srv_path
> as an argument, rtrs_srv_destroy_once_sysfs_root_folders() dereferences it
> internally to access srv_path->srv. If kobject_put() has already freed
> srv_path, this results in a use-after-free.
> 
> Move rtrs_srv_destroy_once_sysfs_root_folders() before kobject_put(), so
> srv_path remains valid while the helper accesses it.

This still doesn't answer my question: how can you access memory referenced
by the srv_path pointer after it has been freed?

  1612         rtrs_srv_destroy_path_files(srv_path); <--- you released memory pointed by srv_path here
  1613
  1614         /* Notify upper layer if we are the last path */
  1615         rtrs_srv_path_down(srv_path);          <--- you are accessing memory which was already released.
  1616

Thanks

> 
> This issue was found by a static analysis tool I am developing.
> 
> Fixes: ae4c81644e91 ("RDMA/rtrs-srv: Rename rtrs_srv_sess to rtrs_srv_path")
> Acked-by: Md Haris Iqbal <haris.iqbal@ionos.com>
> Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
> ---
> v2:
>   - Clarify that the use-after-free happens inside
>     rtrs_srv_destroy_once_sysfs_root_folders(), which dereferences srv_path
>     after kobject_put() may have freed it.
>   - No code changes.
> 
>  drivers/infiniband/ulp/rtrs/rtrs-srv-sysfs.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/infiniband/ulp/rtrs/rtrs-srv-sysfs.c b/drivers/infiniband/ulp/rtrs/rtrs-srv-sysfs.c
> index 51727c7d710c..c9ba9d2d0eb3 100644
> --- a/drivers/infiniband/ulp/rtrs/rtrs-srv-sysfs.c
> +++ b/drivers/infiniband/ulp/rtrs/rtrs-srv-sysfs.c
> @@ -295,8 +295,8 @@ int rtrs_srv_create_path_files(struct rtrs_srv_path *srv_path)
>  put_kobj:
>  	kobject_del(&srv_path->kobj);
>  destroy_root:
> -	kobject_put(&srv_path->kobj);
>  	rtrs_srv_destroy_once_sysfs_root_folders(srv_path);
> +	kobject_put(&srv_path->kobj);
>  
>  	return err;
>  }
> @@ -312,8 +312,8 @@ void rtrs_srv_destroy_path_files(struct rtrs_srv_path *srv_path)
>  
>  	if (srv_path->kobj.state_in_sysfs) {
>  		sysfs_remove_group(&srv_path->kobj, &rtrs_srv_path_attr_group);
> -		kobject_put(&srv_path->kobj);
>  		rtrs_srv_destroy_once_sysfs_root_folders(srv_path);
> +		kobject_put(&srv_path->kobj);
>  	}
>  
>  }
> -- 
> 2.43.0
>