netdev - Re: [PATCH bpf-next] net: Don't uninstall an XDP program when none is installed

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Date:   Wed, 10 Jul 2019 11:16:05 +0000
From:   Maxim Mikityanskiy <maximmi@...lanox.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
CC:     Daniel Borkmann <daniel@...earbox.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>
Subject: Re: [PATCH bpf-next] net: Don't uninstall an XDP program when none is
 installed

On 2019-06-12 19:14, Maxim Mikityanskiy wrote:
> dev_change_xdp_fd doesn't perform any checks in case it uninstalls an
> XDP program. It means that the driver's ndo_bpf can be called with
> XDP_SETUP_PROG asking to set it to NULL even if it's already NULL. This
> case happens if the user runs `ip link set eth0 xdp off` when there is
> no XDP program attached.
> 
> The drivers typically perform some heavy operations on XDP_SETUP_PROG,
> so they all have to handle this case internally to return early if it
> happens. This patch puts this check into the kernel code, so that all
> drivers will benefit from it.
> 
> Signed-off-by: Maxim Mikityanskiy <maximmi@...lanox.com>
> ---
> Björn, please take a look at this, Saeed told me you were doing
> something related, but I couldn't find it. If this fix is already
> covered by your work, please tell about that.
> 
>   net/core/dev.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 66f7508825bd..68b3e3320ceb 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -8089,6 +8089,9 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
>   			bpf_prog_put(prog);
>   			return -EINVAL;
>   		}
> +	} else {
> +		if (!__dev_xdp_query(dev, bpf_op, query))
> +			return 0;
>   	}
>   
>   	err = dev_xdp_install(dev, bpf_op, extack, flags, prog);
> 

Alexei, so what about this patch? It's marked as "Changed Requested" in 
patchwork, but Jakub's point looks resolved - I don't see any changes 
required from my side.