Hello Grzegorz, On 1/25/22 16:22, Grzegorz Szpetkowski wrote: > Dear Maintainers, > > According to packet(7), whenever raw packet is created by socket(), > it's immediately running, meaning that internal packet_rcv() handler > will be triggered and socket buffer will begin allocation of sk_buff > until sk_rcvbuf limit is reached. > > However, by examination of kernel's internal handler packet_create() > it looks that kernel handles case of zero protocol in a special > manner. > When packet_create() is called with arg protocol = 0, > __register_prot_hook is not executed, meaning running state is still 0 > and most notably, packet handler is not added to kernel list (vide > dev_add_pack). > > I found this behavior invaluable for solving a subtle issue. When > process creates raw packet socket to listen for (let's say) all > protocols, but limited to a single network interface, then while this > interface can set by bind, it may to be too late due to preemption > (e.g. if real-time scheduling is used) and/or high-rate of packets on > other interfaces, meaning that undesired packets (any count) may be > pulled into the socket buffer. > > The proposed patch to define behavior when protocol is to zero with socket(). > Please review. > > Signed-off-by: Grzegorz Szpetkowski gszpetkowski@xxxxxxxxx > > diff --git a/man7/packet.7 b/man7/packet.7 > index 706efbb54..461444c43 100644 > --- a/man7/packet.7 > +++ b/man7/packet.7 > @@ -47,6 +47,9 @@ is set to > then all protocols are received. > All incoming packets of that protocol type will be passed to the packet > socket before they are passed to the protocols implemented in the kernel. > +When protocol is set to zero, then no packets are received until > +.BR bind (2) > +specifies allowed protocol or to receive all protocols.man There's something wrong in that line, or I'm not understanding it. Could you please review it? Thanks, Alex > .PP > In order to create a packet socket, a process must have the > .B CAP_NET_RAW > > Thanks, > Grzegorz
