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604d13c97f
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> Signed-off-by: David S. Miller <davem@davemloft.net> |
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