netdev - Re: [PATCH net 1/3] bpf, mlx5: fix mlx5e_create

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Date:   Mon, 14 Nov 2016 20:15:32 +0200
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     Daniel Borkmann <daniel@...earbox.net>, <davem@...emloft.net>
CC:     <alexei.starovoitov@...il.com>, <bblanco@...mgrid.com>,
        <tariqt@...lanox.com>, <zhiyisun@...il.com>, <ranas@...lanox.com>,
        <netdev@...r.kernel.org>
Subject: Re: [PATCH net 1/3] bpf, mlx5: fix mlx5e_create_rq taking reference
 on prog



On 11/14/2016 02:43 AM, Daniel Borkmann wrote:
> In mlx5e_create_rq(), when creating a new queue, we call bpf_prog_add() but
> without checking the return value. bpf_prog_add() can fail, so we really

Didn't know this, thanks for noticing, I wonder why taking a reference for an object would fail ?
especially when someone is requesting from the driver to take a reference to it ndo_xdp_set ?! sounds like a bad design.

Anyway I will check that later.

> must check it. Take the reference right when we assign it to the rq from
> priv->xdp_prog, and just drop the reference on error path. Destruction in
> mlx5e_destroy_rq() looks good, though.
> 
> Fixes: 86994156c736 ("net/mlx5e: XDP fast RX drop bpf programs support")
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> ---
>  drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 14 +++++++++++---
>  kernel/bpf/syscall.c                              |  1 +
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> index 84e8b25..2b83667 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> @@ -489,7 +489,16 @@ static int mlx5e_create_rq(struct mlx5e_channel *c,
>  	rq->channel = c;
>  	rq->ix      = c->ix;
>  	rq->priv    = c->priv;
> +
>  	rq->xdp_prog = priv->xdp_prog;

Why keeping this assignment ? just test priv->xdp_prog.

> +	if (rq->xdp_prog) {
> +		rq->xdp_prog = bpf_prog_inc(rq->xdp_prog);
> +		if (IS_ERR(rq->xdp_prog)) {
> +			err = PTR_ERR(rq->xdp_prog);
> +			rq->xdp_prog = NULL;
> +			goto err_rq_wq_destroy;
> +		}
> +	}

Try this, simpler and less indentations:
 
rq->xdp_prog = priv->xdp_prog ? bpf_prog_inc(priv->xdp_prog) : NULL;
if (IS_ERR(rq->xdp_prog)) {
	err = PTR_ERR(rq->xdp_prog);
	rq->xdp_prog = NULL;
	goto err_rq_wq_destroy;
}

Saeed.