Some code to reproduce this is at https://github.com/craig65535/mcast-exmpl.
The kernel module hooks TCP connects via a jprobe, and multicasts a generic netlink message on every connect. So after insmod'ing the module, just connect anywhere to send a multicast. The client receives multicasts, even when it's not running as root. Again, the documentation (man 7 netlink) does not agree with this. Is this just a documentation bug, or a real bug? On Fri, Mar 6, 2015 at 7:08 PM, Craig Davison <craig65...@gmail.com> wrote: > I wrote a kernel module that sends generic Netlink multicasts, and > wrote a userland client using libmnl that receives them. > > That all works fine, but my client works even when it's not the root user. > > man 7 netlink says: > > Only processes with an effective UID of 0 or the CAP_NET_ADMIN capability > may send or listen to a netlink multicast group. > > The listen part of this is seemingly not true. I've tried this on > kernels 3.13 (Ubuntu 14.04), 2.6.32 (CentOS 6) and 2.6.18 (CentOS 5). > > Is this a bug? > > If not: I know that restricting receiving generic netlink commands > incoming to the kernel to being only from root is possible with > GENL_ADMIN_PERM flag, but is it possible to send multicasts from the > kernel that can only be received by root? > > Thank you -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
