From: Nicolas Dichtel <nicolas.dichtel@6wind•com>
To: Daniel Borkmann <dborkman@redhat•com>, davem@davemloft•net
Cc: netdev@vger•kernel.org, Jakub Zawadzki <darkjames-ws@darkjames•pl>
Subject: Re: [PATCH net-next v3 2/2] netlink: specify netlink packet direction for nlmon
Date: Mon, 23 Dec 2013 18:46:51 +0100 [thread overview]
Message-ID: <52B8770B.60009@6wind.com> (raw)
In-Reply-To: <1387805756-21121-3-git-send-email-dborkman@redhat.com>
Le 23/12/2013 14:35, Daniel Borkmann a écrit :
> In order to facilitate development for netlink protocol dissector,
> fill the unused field skb->pkt_type of the cloned skb with a hint
> of the address space of the new owner (receiver) socket in the
> notion of "to kernel" resp. "to user".
>
> At the time we invoke __netlink_deliver_tap_skb(), we already have
> set the new skb owner via netlink_skb_set_owner_r(), so we can use
> that for netlink_is_kernel() probing.
>
> In normal PF_PACKET network traffic, this field denotes if the
> packet is destined for us (PACKET_HOST), if it's broadcast
> (PACKET_BROADCAST), etc.
>
> As we only have 3 bit reserved, we can use the value (= 6) of
> PACKET_FASTROUTE as it's _not used_ anywhere in the whole kernel
> and not supported anywhere, and packets of such type were never
> exposed to user space, so there are no overlapping users of such
> kind. Thus, as wished, that seems the only way to make both
> PACKET_* values non-overlapping and therefore device agnostic.
>
> By using those two flags for netlink skbs on nlmon devices, they
> can be made available and picked up via sll_pkttype (previously
> unused in netlink context) in struct sockaddr_ll. We now have
> these two directions:
>
> - PACKET_USER (= 6) -> to user space
> - PACKET_KERNEL (= 7) -> to kernel space
>
> Partial `ip a` example strace for sa_family=AF_NETLINK with
> detected nl msg direction:
>
> syscall: direction:
> sendto(3, ...) = 40 /* to kernel */
> recvmsg(3, ...) = 3404 /* to user */
> recvmsg(3, ...) = 1120 /* to user */
> recvmsg(3, ...) = 20 /* to user */
> sendto(3, ...) = 40 /* to kernel */
> recvmsg(3, ...) = 168 /* to user */
> recvmsg(3, ...) = 144 /* to user */
> recvmsg(3, ...) = 20 /* to user */
>
> Signed-off-by: Daniel Borkmann <dborkman@redhat•com>
> Signed-off-by: Jakub Zawadzki <darkjames-ws@darkjames•pl>
> ---
> v1->v2:
> - let PACKET_* values not overlap as requested by Dave
> v2->v3:
> - fixed typo in comment spotted by Nicolas, thanks
>
> include/uapi/linux/if_packet.h | 4 +++-
> net/netlink/af_netlink.c | 2 ++
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/if_packet.h b/include/uapi/linux/if_packet.h
> index e9d844c..06e2a28 100644
> --- a/include/uapi/linux/if_packet.h
> +++ b/include/uapi/linux/if_packet.h
> @@ -26,8 +26,10 @@ struct sockaddr_ll {
> #define PACKET_MULTICAST 2 /* To group */
> #define PACKET_OTHERHOST 3 /* To someone else */
> #define PACKET_OUTGOING 4 /* Outgoing of any type */
> -/* These ones are invisible by user level */
> #define PACKET_LOOPBACK 5 /* MC/BRD frame looped back */
> +#define PACKET_USER 6 /* To user space */
> +#define PACKET_KERNEL 7 /* To kernel space */
> +/* Unused, PACKET_FASTROUTE and PACKET_LOOPBACK are invisible to user space */
> #define PACKET_FASTROUTE 6 /* Fastrouted frame */
Sorry to insist, I just try to understand. Why not removing the definition of
PACKET_FASTROUTE?
Or have a name like PACKET_NL_USER to document the difference between both
cases?
next prev parent reply other threads:[~2013-12-23 17:46 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-23 13:35 [PATCH net-next v3 0/2] nlmon updates Daniel Borkmann
2013-12-23 13:35 ` [PATCH net-next v3 1/2] netlink: only do not deliver to tap when both sides are kernel sks Daniel Borkmann
2013-12-23 13:35 ` [PATCH net-next v3 2/2] netlink: specify netlink packet direction for nlmon Daniel Borkmann
2013-12-23 17:46 ` Nicolas Dichtel [this message]
2013-12-23 17:54 ` Daniel Borkmann
2013-12-31 18:50 ` David Miller
2014-01-01 4:16 ` Daniel Borkmann
2013-12-31 19:32 ` [PATCH net-next v3 0/2] nlmon updates David Miller
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