netdev - Re: [PATCH] rtnetlink: add needed

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <e742f9e0-671d-4058-99af-c3e38b73ec0d@iogearbox.net>
Date: Mon, 15 Sep 2025 18:49:55 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Alasdair McWilliam <alasdair@...illiam.dev>, netdev@...r.kernel.org
Cc: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH] rtnetlink: add needed_{head,tail}room attributes

Hi Alasdair,

On 9/15/25 6:32 PM, Alasdair McWilliam wrote:
> Various network interface types make use of needed_{head,tail}room values
> to efficiently reserve buffer space for additional encapsulation headers,
> such as VXLAN, Geneve, IPSec, etc. However, it is not currently possible
> to query these values in a generic way.
> 
> Introduce ability to query the needed_{head,tail}room values of a network
> device via rtnetlink, such that applications that may wish to use these
> values can do so.
> 
> Signed-off-by: Alasdair McWilliam <alasdair@...illiam.dev>
> ---
>   include/uapi/linux/if_link.h |  2 ++
>   net/core/rtnetlink.c         | 10 +++++++++-
>   2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
> index 45f56c9f95d9..3b491d96e52e 100644
> --- a/include/uapi/linux/if_link.h
> +++ b/include/uapi/linux/if_link.h
> @@ -379,6 +379,8 @@ enum {
>   	IFLA_DPLL_PIN,
>   	IFLA_MAX_PACING_OFFLOAD_HORIZON,
>   	IFLA_NETNS_IMMUTABLE,
> +	IFLA_HEADROOM,
> +	IFLA_TAILROOM,
>   	__IFLA_MAX
>   };
>   
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index 094b085cff20..c68e20a36daa 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -1326,6 +1326,8 @@ static noinline size_t if_nlmsg_size(const struct net_device *dev,
>   	       + rtnl_devlink_port_size(dev)
>   	       + rtnl_dpll_pin_size(dev)
>   	       + nla_total_size(8)  /* IFLA_MAX_PACING_OFFLOAD_HORIZON */
> +	       + nla_total_size(2)  /* IFLA_HEADROOM */
> +	       + nla_total_size(2)  /* IFLA_TAILROOM */
>   	       + 0;
>   }
>   
> @@ -2091,7 +2093,11 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
>   	    nla_put_u32(skb, IFLA_CARRIER_UP_COUNT,
>   			atomic_read(&dev->carrier_up_count)) ||
>   	    nla_put_u32(skb, IFLA_CARRIER_DOWN_COUNT,
> -			atomic_read(&dev->carrier_down_count)))
> +			atomic_read(&dev->carrier_down_count)) ||
> +	    nla_put_u16(skb, IFLA_HEADROOM,
> +			READ_ONCE(dev->needed_headroom)) ||
> +	    nla_put_u16(skb, IFLA_TAILROOM,
> +			READ_ONCE(dev->needed_tailroom)))
>   		goto nla_put_failure;
>   
>   	if (rtnl_fill_proto_down(skb, dev))
> @@ -2243,6 +2249,8 @@ static const struct nla_policy ifla_policy[IFLA_MAX+1] = {
>   	[IFLA_GSO_IPV4_MAX_SIZE]	= NLA_POLICY_MIN(NLA_U32, MAX_TCP_HEADER + 1),
>   	[IFLA_GRO_IPV4_MAX_SIZE]	= { .type = NLA_U32 },
>   	[IFLA_NETNS_IMMUTABLE]	= { .type = NLA_REJECT },
> +	[IFLA_HEADROOM]		= { .type = NLA_U16 },
> +	[IFLA_TAILROOM]		= { .type = NLA_U16 },

Given this is for dumping only, we'd need to replace NLA_U16 above with NLA_REJECT
like in case of IFLA_NETNS_IMMUTABLE.

Also the Documentation/netlink/specs/rt_link.yaml needs an extension, otherwise lgtm.
$subj should have [PATCH net-next] to indicate the target tree.

Thanks,
Daniel