On Wed, Apr 16, 2014 at 11:51 AM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > On Wed, Apr 16, 2014 at 11:40:44AM -0700, Andy Lutomirski wrote: >> On Wed, Apr 16, 2014 at 11:36 AM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: >> > On Wed, Apr 16, 2014 at 10:29:08AM -0700, Andy Lutomirski wrote: >> > >> > [..] >> >> >> Admittedly cgroups aren't currently as important as uid, but if this >> >> >> changes, then SO_PASSCGROUP, as currently written, will have *exactly* >> >> >> the same problem. >> >> > >> >> > Which is easy to foil by using SO_PEERCGROUP and find out who originally >> >> > opened the socket, which is why that is also available! >> >> >> >> Then please remove SO_PASSCGROUP. >> > >> > SO_PASSCGROUP is important because SO_PEERCGROUP does not work with unix >> > datagram sockets. >> >> Right. I forgot about that. >> >> > >> > Again going back to logging example, if some clients are logging to unix >> > datagram sockets, SO_PASSCGROUP is the only option to figure out cgroup >> > of client. >> >> Hmm. I think that, in your patch, the cgroup that is sent is the >> cgroup of the caller of write/send/sendmsg. What if you changed it to >> use the same cgroup that SO_PEERCRED would use? Would that still >> work? > > No. SO_PEERCRED stores the cgroup information once at the time of > connect(). After that it never changes. > > What if sender changes the cgroup. That information will not be captured. > Also what if multiple client use the same socket fd to writer to logger? > In that case too storing cgroup info in socket will not help. What is the use case of SO_PEERCRED, then? Why can't clients that change cgroup reopen the socket? They're already cgroup-aware. As far as I know, there is probably exactly one client that actually changes cgroups and then tries to log without execing first: systemd (or journald as used by systemd). And this is exactly the component that needs to change to use any new socket option, no matter what. >> > How would it work in logging example? Every time logger receives a >> > message, is it supposed to send another message to client to send >> > SCM_CGROUP? That does not sound right. >> >> No -- just have the logger send the cgroup with every message. Yes, >> it seems silly, but it's probably barely more expensive than with the >> code in your patch. > > So receiver gets the cgroup messages even if it might not want to. There > is no way to say "Hey don't send me SCM_CGROUP's messages". The receiver would only get SCM_CGROUP messages if it set SO_PASSCGROUP. > > Now all loggers need to be modifed to always send SCM_CGROUP messages. And > all other more complicated cases might need a different consideration and > clients and servers will need to be modified accordingly. > > I think it is much simpler to allow passing of cgroup information and > once we figure out some concrete cases where passing of that info is > not desirabe, implement SO_NOPASSCGROUP and modify those *selected few > corner cases* to set this flag on sockets. The problem with SO_NOPASSCGROUP is that the programs that would need to set it are probably already written and don't care about cgroups. --Andy -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
