On Thu, Apr 17, 2014 at 10:52 AM, Simo Sorce <ssorce@xxxxxxxxxx> wrote: > On Thu, 2014-04-17 at 10:26 -0700, Andy Lutomirski wrote: >> On Thu, Apr 17, 2014 at 10:12 AM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: >> > On Thu, Apr 17, 2014 at 09:55:08AM -0700, Andy Lutomirski wrote: >> >> On Thu, Apr 17, 2014 at 9:48 AM, Simo Sorce <ssorce@xxxxxxxxxx> wrote: >> >> > On Thu, 2014-04-17 at 09:37 -0700, Andy Lutomirski wrote: >> >> >> On Thu, Apr 17, 2014 at 9:24 AM, Simo Sorce <ssorce@xxxxxxxxxx> wrote: >> >> >> > On Thu, 2014-04-17 at 09:11 -0700, Andy Lutomirski wrote: >> >> >> >> >> >> >> >> No. The logging daemon thinks it wants to know who the writer is, but >> >> >> >> the logging daemon is wrong. It actually wants to know who composed a >> >> >> >> log message destined to it. The caller of write(2) may or may not be >> >> >> >> the same entity. >> >> >> > >> >> >> > This works both ways, and doesn't really matter, you are *no* better off >> >> >> > w/o this interface. >> >> >> > >> >> >> >> If this form of SO_PASSCGROUP somehow makes it into a pull request for >> >> >> >> Linus, I will ask him not to pull it and/or to revert it. I think >> >> >> >> he'll agree that write(2) MUST NOT care who called it. >> >> >> > >> >> >> > And write() does not, there is no access control check being performed >> >> >> > here. This call is the same as getting the pid of the process and >> >> >> > crawling /proc with that information, just more efficient and race-free. >> >> >> >> >> >> Doing it using the pid of writer is wrong. So is doing it with the >> >> >> cgroup of the writer. The fact that it's even possible to use the pid >> >> >> of the caller of write(2) is a mistake, but that particular mistake >> >> >> is, unfortunately, well-enshrined in history. >> >> >> >> >> >> > >> >> >> > I repeat, it is *not* access control. >> >> >> > >> >> >> >> >> >> Sure it is. >> >> >> >> >> >> Either correct attribution of logs doesn't matter, in which case it >> >> >> makes little difference how you do it, or it does matter, in which >> >> >> case it should be done right. >> >> > >> >> > Well journald can *also* get SO_PEERCGROUP and log anomalies if the 2 >> >> > differ. That is if the log happens on a connected socket. >> >> > >> >> > If the log happens on a unix datagram* then SO_PEERCGROUP is not >> >> > available because there is no connect(), however write() cannot be used >> >> > either, only sendmsg() AFAIK, so the "setuid" binary attack does not >> >> > apply. >> >> > >> >> >> >> Or you could only send SCM_CGROUP when the writer asks sendmsg to send >> >> it, in which case this whole problem goes away. >> > >> > Sending SCM_CGROUP explicitly is also sending cgroup info at write(2) time >> > and if receiver uses that info for access control, it can be problematic. >> > >> >> 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. > > So you are telling me that you want to change all code that writes to > stderr to be changed to use sendmsg() instead of write() in order to get > that information ? No. I'm telling you that I want whoever writes the logging code to change *the logging code* to use sendmsg. > > If you are using datagram sockets then the sender explicitly has to use > sendmsg() already and if a setuid binary can be convinced to send > arbitrary data to an arbitrary datagram sokcet you have bigger problems > in that binary, and said binary will send you whatever cgroup it is in. Really? --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
