On Thu, Apr 17, 2014 at 02:50:23PM -0400, Vivek Goyal wrote: > On Thu, Apr 17, 2014 at 02:23:33PM -0400, Simo Sorce 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. > > So what would be the protocol here? When should somebody send an > SCM_CGROUP message using sendmsg()? I don't know how it will even be used for systemd logging case. systemd provides various ways to connect stdout of services. So say a service's stdout is connected to a connected datagram socket and all printf() messages to stdout are being logged by receiver in journal. Now how would sender know that it is supposed to send SCM_CGROUP? One needs to modify printf() now? Thanks Vivek -- 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
