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. You do realize that we have been speaking in hypothetical for a while now ? Even without doing the SO_PEERCRED, you are not going to fool the log, as it gathers a ton of other info about the process, and cgroup is just one of the infos used to classify the log. There are also credentials, pid, and a lot of other things. Even if a setuid binary could be tricked to send a message with an "impostor" cgroup don't you think you'd see other things out of place ? (wrong uid, wrong pid, etc...). What I am telling you is that userspace has all the tools it needs to not get fooled, as long as cgroup information retrieved via SO_PASSCGROUP is not uniquely used to authenticate a peer process for connected sockets. Simo. -- 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
