Re: [PATCH net 1/2] net/mlx5e: psp: Fix invalid access on PSP dev registration fail

[Jakub Kicinski <kuba@kernel.org>]

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---
net/mlx5e: psp: Fix invalid access on PSP dev registration fail

This commit updates PSP device registration to use a local variable,
only saving the PSP device pointer if psp_dev_create() succeeds. This
prevents an error pointer from being stored in priv->psp->psp.

> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_accel/psp.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_accel/psp.c
[ ... ]
> @@ -1070,29 +1070,37 @@ static struct psp_dev_ops mlx5_psp_ops = {
[ ... ]
>  void mlx5e_psp_register(struct mlx5e_priv *priv)
>  {
> +	struct mlx5e_psp *psp = priv->psp;
> +	struct psp_dev *psd;
> +
[ ... ]
> -	priv->psp->psp = psp_dev_create(priv->netdev, &mlx5_psp_ops,
> -					&priv->psp->caps, NULL);
> -	if (IS_ERR(priv->psp->psp))
> +	psd = psp_dev_create(priv->netdev, &mlx5_psp_ops, &psp->caps, NULL);
> +	if (IS_ERR(psd)) {
>  		mlx5_core_err(priv->mdev, "PSP failed to register due to %pe\n",
> -			      priv->psp->psp);
> +			      psd);
> +		return;
> +	}
> +	psp->psp = psd;
>  }

When psp_dev_create() fails, this function now returns without setting
psp->psp, leaving it as NULL. However, priv->psp remains allocated and
non-NULL.

Does this leave the RX datapath vulnerable to a NULL pointer dereference?

If priv->psp is non-NULL, the NIC RX initialization path can still call
mlx5_accel_psp_fs_init_rx_tables(), which creates hardware flow steering
rules to intercept UDP traffic.

If a UDP packet triggers these rules, the hardware flags the CQE with
MLX5E_PSP_MARKER_BIT. The RX fast-path sees the marker and invokes
mlx5e_psp_offload_handle_rx_skb(), which dereferences the pointer
unconditionally:

u16 dev_id = priv->psp->psp->id;

Since priv->psp->psp is NULL, this will cause a kernel panic. Should
priv->psp be cleaned up, or the error propagated, to prevent flow rules
from being installed when registration fails?
-- 
pw-bot: cr