[lxc-devel] User namespaces

[Dwight Engen]

Hi Eric, any chance you've had a moment to mull this over any more?
I've also CC'ed Jiri since he is listed in MAINTAINERS for the TTY
layer :)

On Wed, 6 Mar 2013 09:58:53 -0600
Serge Hallyn <serge.hallyn at ubuntu.com> wrote:

> Quoting Dwight Engen (dwight.engen at oracle.com):
> > On Mon, 25 Feb 2013 20:26:21 -0800
> > ebiederm at xmission.com (Eric W. Biederman) wrote:
> ...
> > > For pty's since they only have the single device node.  We can
> > > probably do kuid_has_mapping and kgid_has_mapping to see if we
> > > should have super user privileges over the pty.  But that is
> > > specific to ptys on /dev/pts. Normal devices potentially can have
> > > device nodes with different permissions in different places so we
> > > can't figure out an owner for the device.
> > > 
> > > Eric
> > > 
> > 
> > Yeah, I agree we don't want something pty specific. The following
> > patch assumes we define a tty as belonging to the user ns of its
> > session leader (and if it doesn't have one then to init_user_ns) as
> > you first suggested. I added locking which avoids the race with
> > disassociate_tty() and ensures the user ns doesn't get unrefed by
> > way of put_pid(tty->session).
> > 
> > Note that I think TIOCVHANGUP should be checking for
> > CAP_SYS_TTY_CONFIG instead of CAP_SYS_ADMIN to be consistent with
> > vhangup(2), but I did not change that in the refactoring here.
> > 
> > --
> > 
> > From 697f842ffc709312e5775e3d1d0782079c3070dc Mon Sep 17 00:00:00
> > 2001 From: Dwight Engen <dwight.engen at oracle.com>
> > Date: Fri, 1 Mar 2013 13:49:58 -0500
> > Subject: [PATCH] make vhangup and TIOCVHANGUP namespace aware
> > 
> > Signed-off-by: Dwight Engen <dwight.engen at oracle.com>
> 
> It looks good to me.  Eric?
> 
> Acked-by: Serge E. Hallyn <serge.hallyn at ubuntu.com>
> 
> > ---
> >  drivers/tty/tty_io.c | 36 ++++++++++++++++++++++++++++++------
> >  fs/open.c            |  6 +-----
> >  include/linux/tty.h  |  2 +-
> >  3 files changed, 32 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> > index a057db8..764d4e7 100644
> > --- a/drivers/tty/tty_io.c
> > +++ b/drivers/tty/tty_io.c
> > @@ -104,6 +104,7 @@
> >  
> >  #include <linux/kmod.h>
> >  #include <linux/nsproxy.h>
> > +#include <linux/pid_namespace.h>
> >  
> >  #undef TTY_DEBUG_HANGUP
> >  
> > @@ -722,6 +723,29 @@ void tty_vhangup(struct tty_struct *tty)
> >  
> >  EXPORT_SYMBOL(tty_vhangup);
> >  
> > +/**
> > + *	tty_vhangup_check_cap	-	process vhangup
> > checking for capablity
> > + *
> > + *	Perform a vhangup on the given tty
> > + */
> > +
> > +static int tty_vhangup_check_cap(struct tty_struct *tty, int cap)
> > +{
> > +	unsigned long flags;
> > +	int retval = 0;
> > +	struct user_namespace *ns = &init_user_ns;
> > +
> > +	spin_lock_irqsave(&tty->ctrl_lock, flags);
> > +	if (tty->session)
> > +		ns = ns_of_pid(tty->session)->user_ns;
> > +	if (!ns_capable(ns, cap))
> > +		retval = -EPERM;
> > +	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
> > +
> > +	if (!retval)
> > +		tty_vhangup(tty);
> > +	return retval;
> > +}
> >  
> >  /**
> >   *	tty_vhangup_self	-	process vhangup for own
> > ctty @@ -729,15 +753,18 @@ EXPORT_SYMBOL(tty_vhangup);
> >   *	Perform a vhangup on the current controlling tty
> >   */
> >  
> > -void tty_vhangup_self(void)
> > +int tty_vhangup_self(void)
> >  {
> >  	struct tty_struct *tty;
> > +	int retval = 0;
> >  
> >  	tty = get_current_tty();
> >  	if (tty) {
> > -		tty_vhangup(tty);
> > +		retval = tty_vhangup_check_cap(tty,
> > CAP_SYS_TTY_CONFIG); tty_kref_put(tty);
> >  	}
> > +
> > +	return retval;
> >  }
> >  
> >  /**
> > @@ -2710,10 +2737,7 @@ long tty_ioctl(struct file *file, unsigned
> > int cmd, unsigned long arg) case TIOCSETD:
> >  		return tiocsetd(tty, p);
> >  	case TIOCVHANGUP:
> > -		if (!capable(CAP_SYS_ADMIN))
> > -			return -EPERM;
> > -		tty_vhangup(tty);
> > -		return 0;
> > +		return tty_vhangup_check_cap(tty, CAP_SYS_ADMIN);
> >  	case TIOCGDEV:
> >  	{
> >  		unsigned int ret =
> > new_encode_dev(tty_devnum(real_tty)); diff --git a/fs/open.c
> > b/fs/open.c index 9b33c0c..19ac16e 100644
> > --- a/fs/open.c
> > +++ b/fs/open.c
> > @@ -1059,11 +1059,7 @@ EXPORT_SYMBOL(sys_close);
> >   */
> >  SYSCALL_DEFINE0(vhangup)
> >  {
> > -	if (capable(CAP_SYS_TTY_CONFIG)) {
> > -		tty_vhangup_self();
> > -		return 0;
> > -	}
> > -	return -EPERM;
> > +	return tty_vhangup_self();
> >  }
> >  
> >  /*
> > diff --git a/include/linux/tty.h b/include/linux/tty.h
> > index 8db1b56..c9d0e9c 100644
> > --- a/include/linux/tty.h
> > +++ b/include/linux/tty.h
> > @@ -379,7 +379,7 @@ extern int tty_signal(int sig, struct
> > tty_struct *tty); extern void tty_hangup(struct tty_struct *tty);
> >  extern void tty_vhangup(struct tty_struct *tty);
> >  extern void tty_vhangup_locked(struct tty_struct *tty);
> > -extern void tty_vhangup_self(void);
> > +extern int tty_vhangup_self(void);
> >  extern void tty_unhangup(struct file *filp);
> >  extern int tty_hung_up_p(struct file *filp);
> >  extern void do_SAK(struct tty_struct *tty);
> > -- 
> > 1.7.12.3
> >