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. Thanks, Andrew -- 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
