On Thu, Apr 17, 2014 at 11:23 AM, Simo Sorce <ssorce@xxxxxxxxxx> wrote: > On Thu, 2014-04-17 at 10:35 -0700, Andy Lutomirski wrote: >> On Thu, Apr 17, 2014 at 10:33 AM, Simo Sorce <ssorce@xxxxxxxxxx> wrote: >> > On Thu, 2014-04-17 at 10:26 -0700, Andy Lutomirski wrote: >> >> >> >> Not really. write(2) can't send SCM_CGROUP. Callers of sendmsg(2) >> >> who supply SCM_CGROUP are explicitly indicating that they want their >> >> cgroup associated with that message. Callers of write(2) and send(2) >> >> are simply indicating that they have some bytes that they want to >> >> shove into whatever's at the other end of the fd. >> > >> > But there is no attack vector that passes by tricking setuid binaries to >> > write to pre-opened file descriptors on sendmsg(), and for the other >> > cases (connected socket) journald can always cross check with >> > SO_PEERCGROUP, so why do we care again ? >> >> Because the proposed code does not do what I described, at least as >> far I as I can tell. > > Ok let me backtrack, apparently if you explicitly use connect() on a > datagram socket then you *can* write() (thanks to Vivek for checking > this). > > So you can trick something to write() to it but you can't do > SO_PEERCGROUP on the other side, because it is not really a connected > socket, the connection is only faked on the sender side by constructing > sendmsg() messages with the original address passed into connect(). > > So given this unfortunate circumstance, requiring the client to > explicitly pass cgroup data on unix datagram sockets may be an > acceptable request IMO. > > Perhaps this could be done with a sendmsg() header flag or simplified > ancillary data even, rather than forcing the sender process to retrieve > and construct the whole information which is already available in > kernel. It seems reasonable to me to have the sender give a blank SCM_CGROUP and to let the kernel populate it. I'm still a bit vague on what happens if the sender is in two different cgroups. Which one wins? Presumably the unified hierarchy one if one of them is in use, but I haven't kept track of all the changes there. --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
