Re: [PATCH] IB/mlx4: Fix refcount leak in add_port() error path

[Leon Romanovsky <leon@kernel.org>]

On Sat, Apr 11, 2026 at 05:16:26PM +0800, Guangshuo Li wrote:
> After kobject_init_and_add(), the lifetime of the embedded struct
> kobject is expected to be managed through the kobject core reference
> counting.
> 
> In add_port(), if kobject_init_and_add() fails, the error path frees p
> directly instead of releasing the kobject reference with kobject_put().
> This may leave the reference count of the embedded struct kobject
> unbalanced, resulting in a refcount leak and potentially leading to a
> use-after-free.
> 
> Fix this by using kobject_put(&p->kobj) in the kobject_init_and_add()
> failure path.

The analysis is correct, the implementation is wrong.

> 
> Fixes: c1e7e466120b ("IB/mlx4: Add iov directory in sysfs under the ib device")
> Cc: stable@vger.kernel.org
> Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
> ---
>  drivers/infiniband/hw/mlx4/sysfs.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/hw/mlx4/sysfs.c b/drivers/infiniband/hw/mlx4/sysfs.c
> index 88f534cf690e..15b36b9e4bd6 100644
> --- a/drivers/infiniband/hw/mlx4/sysfs.c
> +++ b/drivers/infiniband/hw/mlx4/sysfs.c
> @@ -642,7 +642,7 @@ static int add_port(struct mlx4_ib_dev *dev, int port_num, int slave)
>  				   kobject_get(dev->dev_ports_parent[slave]),
>  				   "%d", port_num);
>  	if (ret)
> -		goto err_alloc;
> +		goto err_kobj;
>  
>  	p->pkey_group.name  = "pkey_idx";
>  	p->pkey_group.attrs =
> @@ -689,6 +689,11 @@ static int add_port(struct mlx4_ib_dev *dev, int port_num, int slave)
>  	kobject_put(dev->dev_ports_parent[slave]);
>  	kfree(p);

This needs to be changed to: “kobject_put(&p->kobj);”.

>  	return ret;
> +
> +err_kobj:
> +	kobject_put(&p->kobj);

I’m also wondering why we don’t call kobject_put() in the port deletion
path as well.

Thanks

> +	return ret;
> +
>  }
>  
>  static int register_one_pkey_tree(struct mlx4_ib_dev *dev, int slave)
> -- 
> 2.43.0
>