On Wed, Jul 8, 2015 at 9:10 AM, Andrew Vagin <avagin@xxxxxxxx> wrote: > On Tue, Jul 07, 2015 at 08:56:37AM -0700, Andy Lutomirski wrote: >> On Tue, Jul 7, 2015 at 8:43 AM, Andrew Vagin <avagin@xxxxxxxx> wrote: >> > On Mon, Jul 06, 2015 at 10:10:32AM -0700, Andy Lutomirski wrote: >> >> On Mon, Jul 6, 2015 at 1:47 AM, Andrey Vagin <avagin@xxxxxxxxxx> wrote: >> >> > Currently we use the proc file system, where all information are >> >> > presented in text files, what is convenient for humans. But if we need >> >> > to get information about processes from code (e.g. in C), the procfs >> >> > doesn't look so cool. >> >> > >> >> > From code we would prefer to get information in binary format and to be >> >> > able to specify which information and for which tasks are required. Here >> >> > is a new interface with all these features, which is called task_diag. >> >> > In addition it's much faster than procfs. >> >> > >> >> > task_diag is based on netlink sockets and looks like socket-diag, which >> >> > is used to get information about sockets. >> >> >> >> I think I like this in principle, but I have can see a few potential >> >> problems with using netlink for this: >> >> >> >> 1. Netlink very naturally handles net namespaces, but it doesn't >> >> naturally handle any other kind of namespace. In fact, the taskstats >> >> code that you're building on has highly broken user and pid namespace >> >> support. (Look for some obviously useless init_user_ns and >> >> init_pid_ns references. But that's only the obvious problem. That >> >> code calls current_user_ns() and task_active_pid_ns(current) from >> >> .doit, which is, in turn, called from sys_write, and looking at >> >> current's security state from sys_write is a big no-no.) >> >> >> >> You could partially fix it by looking at f_cred's namespaces, but that >> >> would be a change of what it means to create a netlink socket, and I'm >> >> not sure that's a good idea. >> > >> > If I don't miss something, all problems around pidns and userns are >> > related with multicast functionality. task_diag is using >> > request/response scheme and doesn't send multicast packets. >> >> It has nothing to do with multicast. task_diag needs to know what >> pidns and userns to use for a request, but netlink isn't set up to >> give you any reasonably way to do that. A netlink socket is >> fundamentally tied to a *net* ns (it's a socket, after all). But you >> can send it requests using write(2), and calling current_user_ns() >> from write(2) is bad. There's a long history of bugs and >> vulnerabilities related to thinking that current_cred() and similar >> are acceptable things to use in write(2) implementations. >> > > As far as I understand, socket_diag doesn't have this problem, becaus > each socket has a link on a namespace where it was created. > > What if we will pin the current pidns and credentials to a task_diag > socket in a moment when it's created. That's certainly doable. OTOH, if anything does: socket(AF_NETLINK, ...); unshare(CLONE_PID); fork(); then they now have a (minor) security problem. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
