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    SubjectRe: [PATCH] user namespace: make signal.c respect user namespaces
    Quoting Oleg Nesterov (oleg@redhat.com):
    > On 09/25, Serge E. Hallyn wrote:
    > >
    > > Quoting Oleg Nesterov (oleg@redhat.com):
    > > > On 09/23, Serge E. Hallyn wrote:
    > > > >
    > > > > Quoting Oleg Nesterov (oleg@redhat.com):
    > > > > > On 09/23, Serge E. Hallyn wrote:
    > > > > > >
    > > > > > > It looks like I can fix all the
    > > > > > > cases
    > > > > >
    > > > > > except ptrace_signal(). Although we can simply ignore this case, imho.
    > > > >
    > > > > ptrace_signal() calls send_signal() though.
    > > >
    > > > Confused... I meant the "if (signr != info->si_signo)" case. This is
    > > > simple, and I only meant that this case is not that important.
    > >
    > > Yes, that's the case I was talking about. That then proceeds through
    > > send_signal().
    >
    > It doesn't? I am even more confuused. Anyway, your patch adds map_cred_ns()
    > into ptrace_signal().
    >
    > > The whole new patch (so far only compile-tested) is below.
    >
    > Perhaps I missed something, but it looks overcomplicated. I was thinking
    > about the (uncompiled/untested) simple patch below (it ignores ptrace_signal
    > for clarity).
    >
    > And note that this way we do not need to modify do_notify_parent*()
    > or ipc/mqueue.c:__do_notify() (your patch doesn't cover the latter).
    > Unless I missed something of course.
    >
    > And we do not need to handle the SEND_SIG_NOINFO case separately.
    >
    >
    > However, we still have the problems with sigqueueinfo,
    >
    > > > > > > by checking whether si_fromuser(info)
    > > > > >
    > > > > > I am not sure... sys_rt_queueinfo() is nasty. Plus we have to handle
    > > > > > the "fromkernel" case too. May be we can ignore this too.
    > > > >
    > > > > sys_rt_tgsigqueueinfo() still seems to go through send_signal().
    > > >
    > > > Yes. But how can you fix si_uid? We do not even know if it exists.
    > > > Please look at siginfo/_uid, there is a union. We can't know what
    > > > the caller of sys_rt_sigqueueinfo() puts in this location.
    > >
    > > But it's a union alongside the pid.
    >
    > Again, I do not understand... Yes, we have the same problem with
    >
    > if (from_ancestor_ns)
    > q->info.si_pid = 0;
    >
    > This was discussed, we do not know what we can do. My point was, this
    > change is not sigqueueinfo-friendly too.
    >
    > Oleg.
    >
    > --- x/kernel/signal.c
    > +++ x/kernel/signal.c
    > @@ -1019,6 +1019,27 @@ static inline int legacy_queue(struct si
    > return (sig < SIGRTMIN) && sigismember(&signals->signal, sig);
    > }
    >
    > +static inline fixup_uid(struct siginfo *info, struct task_struct *t)
    > +{
    > +#ifdef CONFIG_USER_NS
    > + if (current_user_ns() == task_cred_xxx(t, user_ns)))
    > +#endif
    > + return;
    > +
    > + if (SI_FROMKERNEL(info))
    > + switch (info->si_code & __SI_MASK) {
    > + default:
    > + return;
    > +
    > + case __SI_CHLD:

    After looking a bit more, I really think the __SI_CHLD case just needs to
    always be converted at the callers (i.e. do_notify_parent).

    > + case __SI_MESGQ:

    This can be done like this, but if this is going to be the only case of
    a SI_FROMKERNEL not being converted at the caller, and there is aiui only
    one caller (__do_notivy in ipc/mmqueue.c), it seems better to just have
    fixup_uid() always return for SI_FROMKERNEL(info).

    Does that sound ok?

    If so, I'll whip up the patch and send it out after some testing. (If
    not, I'll try to better understand :)


    > + break;
    > + }
    > +
    > + info->si_uid = user_ns_map_uid(task_cred_xxx(t, user_ns),
    > + current_cred(), info->si_uid);
    > +}
    > +
    > static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
    > int group, int from_ancestor_ns)
    > {
    > @@ -1088,6 +1109,9 @@ static int __send_signal(int sig, struct
    > q->info.si_pid = 0;
    > break;
    > }
    > +
    > + fixup_uid(info, t);
    > +
    > } else if (!is_si_special(info)) {
    > if (sig >= SIGRTMIN && info->si_code != SI_USER) {
    > /*
    >

    thanks,
    -serge


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