linux-kernel - Re: user namespace: make signal.c respect user namespaces (v5)

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Message-ID: <m1aa7u2jv1.fsf@fess.ebiederm.org>
Date:	Thu, 17 Nov 2011 19:24:34 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matt Helsley <matthltc@...ibm.com>, richard@....at,
	containers@...ts.linux-foundation.org, eparis@...hat.com,
	oleg@...hat.com, dhowells@...hat.com
Subject: Re: user namespace: make signal.c respect user namespaces (v5)

"Serge E. Hallyn" <serge@...lyn.com> writes:

> ipc/mqueue.c: for __SI_MESQ, convert the uid being sent to recipient's
> user namespace. (new, thanks Oleg)
>
> __send_signal: convert current's uid to the recipient's user namespace
> for any siginfo which is not SI_FROMKERNEL (patch from Oleg, thanks
> again :)
>
> do_notify_parent and do_notify_parent_cldstop: map task's uid to parent's
> user namespace
>
> ptrace_signal maps parent's uid into current's user namespace before
> including in signal to current.  IIUC Oleg has argued that this shouldn't
> matter as the debugger will play with it, but it seems like not converting
> the value currently being set is misleading.
>
> Changelog:
> Sep 20: Inspired by Oleg's suggestion, define map_cred_ns() helper to
> 	simplify callers and help make clear what we are translating
>         (which uid into which namespace).  Passing the target task would
> 	make callers even easier to read, but we pass in user_ns because
> 	current_user_ns() != task_cred_xxx(current, user_ns).
> Sep 20: As recommended by Oleg, also put task_pid_vnr() under rcu_read_lock
> 	in ptrace_signal().
> Sep 23: In send_signal(), detect when (user) signal is coming from an
> 	ancestor or unrelated user namespace.  Pass that on to __send_signal,
> 	which sets si_uid to 0 or overflowuid if needed.
> Oct 12: Base on Oleg's fixup_uid() patch.  On top of that, handle all
> 	SI_FROMKERNEL cases at callers, because we can't assume sender is
> 	current in those cases.
> Nov 10: (mhelsley) rename fixup_uid to more meaningful usern_fixup_signal_uid
> Nov 10: (akpm) make the !CONFIG_USER_NS case clearer
>

> @@ -1088,6 +1117,9 @@ static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
>  				q->info.si_pid = 0;
>  			break;
>  		}
> +
> +		userns_fixup_signal_uid(info, t);

There is a small bug here.  You want to fixup q->info, not info.
Otherwise you might try dereferencing one of the special signals and get
a NULL pointer dereference.

Eric

> +
>  	} else if (!is_si_special(info)) {
>  		if (sig >= SIGRTMIN && info->si_code != SI_USER) {
>  			/*
--
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