netdev - Re: [PATCH v6 1/4] udp_tunnel: add config option to bind to a device

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Message-ID: <20181130143100.GA7623@bistromath.localdomain>
Date:   Fri, 30 Nov 2018 15:31:00 +0100
From:   Sabrina Dubroca <sd@...asysnail.net>
To:     Alexis Bauvin <abauvin@...leway.com>
Cc:     dsa@...ulusnetworks.com, roopa@...ulusnetworks.com,
        stephen@...workplumber.org, netdev@...r.kernel.org,
        akherbouche@...leway.com
Subject: Re: [PATCH v6 1/4] udp_tunnel: add config option to bind to a device

2018-11-27, 14:05:42 +0100, Alexis Bauvin wrote:
> diff --git a/net/ipv4/udp_tunnel.c b/net/ipv4/udp_tunnel.c
> index 6539ff15e9a3..dc68e15a4f72 100644
> --- a/net/ipv4/udp_tunnel.c
> +++ b/net/ipv4/udp_tunnel.c
> @@ -20,6 +20,16 @@ int udp_sock_create4(struct net *net, struct udp_port_cfg *cfg,
>  	if (err < 0)
>  		goto error;
>  
> +	if (cfg->bind_ifindex) {
> +		struct net_device *dev;
> +
> +		dev = __dev_get_by_index(net, cfg->bind_ifindex);

Quoting from net/core/dev.c:

 *	[...]                                    The device has not
 *	had its reference counter increased so the caller must be careful
 *	about locking. The caller must hold either the RTNL semaphore
 *	or @dev_base_lock.
 */

which is the case for VXLAN (and GENEVE) during ndo_open, but I don't
think other UDP tunnels (FOU, L2TP) are holding RTNL when they call
udp_sock_create(). dev_get_by_index() + dev_put() should be safe.

Also, I don't think it's a problem with vxlan, but this could handle
the case where __dev_get_by_index returns NULL.

> +		err = kernel_setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE,
> +					dev->name, strlen(dev->name) + 1);
> +		if (err < 0)
> +			goto error;
> +	}
> +
>  	udp_addr.sin_family = AF_INET;
>  	udp_addr.sin_addr = cfg->local_ip;
>  	udp_addr.sin_port = cfg->local_udp_port;

-- 
Sabrina