Messages in this thread | | | Date | Fri, 20 Feb 2009 01:28:51 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 7/7][v8] SI_USER: Masquerade si_pid when crossing pid ns boundary |
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On 02/19, Eric W. Biederman wrote: > > Oleg Nesterov <oleg@redhat.com> writes: > > > On 02/19, Eric W. Biederman wrote: > >> > >> Oleg Nesterov <oleg@redhat.com> writes: > >> > > >> > SI_FROMUSER() == T, unless we have more (hopefully not) in-kernel > >> > users which send SI_FROMUSER() signals, .si_pid must be valid? > >> > >> So the argument is that while things such as force_sig_info(SIGSEGV) > >> don't have a si_pid we don't care because from_ancestor_ns == 0. > >> > >> Interesting. Then I don't know if we have any kernel senders > >> that cross the namespace boundaries. > >> > >> That said I still object to this code. > >> > >> sys_kill(-pgrp, SIGUSR1) > >> kill_something_info(SIGUSR1, &info, 0) > >> __kill_pgrp_info(SIGUSR1, &info task_pgrp(current)) > >> group_send_sig_info(SIGUSR1, &info, tsk) > >> __group_send_sig_info(SIGUSR1, &info, tsk) > >> send_signal(SIGUSR1, &info, tsk, 1) > >> __send_signal(SIGUSR1, &info, tsk, 1) > >> > >> > >> Process groups and sessions can have processes in multiple pid > >> namespaces, which is very useful for not messing up your controlling > >> terminal. > >> > >> In which case sys_kill cannot possibly set the si_pid value correct > >> and from_ancestor_ns is not enough either. > > > > (I know, I shouldn't reply today because I am already sleeping ;) > > > > Why? send_signal() should calculate the correct value of > > from_parent and pass it to __send_signal(). If it is true, then > > we clear .si_pid in the copied siginfo (which was already queued). > > We don't mangle the original siginfo. > > > > This happens for each process we send the signal. > > > > Or I misunderstood you? > > Suppose I have 3 processes in a process group in three separate pid > namespaces. > > Looking from the init pid namespace I have: > pid pgrp ppid > 10 10 1 > 11 10 10 > 12 10 11 > > Looking from the pid namespace of pid 11 I have: > pid pgrp ppid > 0 0 0 > 1 0 0 > 2 0 1 > > Looking from the pid namespace of pid 12 I have: > pid pgrp ppid > 0 0 0 > 0 0 0 > 1 0 0 > > So if the process with pid 12 in the initial pid namespace > sends to process group 0.
But this is the different problem, it is not that we clear si_pid while we shouldn't, just the .si_pid passed from kill_something_info() is not right.
Personally, I think we should not allow to send signals outside our namespace (except SIGCHLD on exit), this looks just wrong to me. And some time ago copy_process(CLONE_PID) did "setsid".
Hmm... that was changed by your commit 5cd17569fd0eeca510735e63a6061291e3971bf6. And while I agree with this commit, I think that cinit should do sys_setsid() itself to detach itself from the parent namespace.
Or. We can fix the case you described. We can move "si_pid = task_tgid_vnr()" from sys_kill/do_tkill/etc to send_signal(), it can calculate the correct .si_pid looking at sender/receiver namespaces.
Oleg.
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