linux-kernel - Re: [PATCH] user namespace: make signal.c respect user namespaces

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Date:	Mon, 26 Sep 2011 18:06:19 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Serge E. Hallyn" <serge.hallyn@...onical.com>
Cc:	lkml <linux-kernel@...r.kernel.org>, richard@....at,
	Andrew Morton <akpm@...gle.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Tejun Heo <tj@...nel.org>, serge@...lyn.com
Subject: Re: [PATCH] user namespace: make signal.c respect user namespaces

On 09/25, Serge E. Hallyn wrote:
>
> Quoting Oleg Nesterov (oleg@...hat.com):
> > On 09/23, Serge E. Hallyn wrote:
> > >
> > > Quoting Oleg Nesterov (oleg@...hat.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:
+			case __SI_MESGQ:
+				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) {
 			/*

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