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Message-ID: <20130209191409.643c3d7f@neptune.home>
Date: Sat, 9 Feb 2013 19:14:09 +0100
From: Bruno Prémont <bonbons@...ux-vserver.org>
To: Corey Minyard <minyard@....org>
Cc: Linux Kernel <linux-kernel@...r.kernel.org>,
Corey Minyard <cminyard@...sta.com>,
containers@...ts.linux-foundation.org
Subject: Re: [PATCH] Move console redirect to pid namespace
CCing containers list
On Fri, 08 February 2013 minyard@....org wrote:
> From: Corey Minyard <cminyard@...sta.com>
>
> The console redirect - ioctl(fd, TIOCCONS) - is not in a namespace,
> thus a container can do a redirect and grab all the I/O on the host
> and all container consoles.
>
> This change puts the redirect in the pid namespace.
>
> Signed-off-by: Corey Minyard <cminyard@...sta.com>
> ---
>
> I'm pretty sure this patch is not correct, but I'm not quite sure the
> best way to fix this. I'm not 100% sure that the pid namespace is the
> right place, but it seemed the most reasonable of all the choices. The
> other obvious choice is the mount namespace, but it didn't seem as good
> a fit.
With recent changes, tying it to init user namespace might even be better.
> The other problem is that I don't think you can call fput() from
> destroy_pid_namespace(). That can be called from interrupt context,
> and I don't think fput() is safe there. I know it's not safe in 3.4
> with the RT patch applied. However, the only way I've come up with to
> fix it is to add a workqueue, and that seems a bit heavy for this.
>
> drivers/tty/tty_io.c | 29 ++++++++++++++++++-----------
> include/linux/pid_namespace.h | 1 +
> kernel/pid_namespace.c | 3 +++
> 3 files changed, 22 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index da9fde8..c93c23d 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -95,6 +95,7 @@
> #include <linux/seq_file.h>
> #include <linux/serial.h>
> #include <linux/ratelimit.h>
> +#include <linux/pid_namespace.h>
>
> #include <linux/uaccess.h>
>
> @@ -503,8 +504,10 @@ static const struct file_operations hung_up_tty_fops = {
> .release = tty_release,
> };
>
> +/*
> + * redirect is in the pid namespace, but we use a global lock.
> + */
> static DEFINE_SPINLOCK(redirect_lock);
> -static struct file *redirect;
>
> /**
> * tty_wakeup - request more data
> @@ -563,15 +566,17 @@ static void __tty_hangup(struct tty_struct *tty)
> int closecount = 0, n;
> unsigned long flags;
> int refs = 0;
> + struct file *redir;
>
> if (!tty)
> return;
>
>
> spin_lock(&redirect_lock);
> - if (redirect && file_tty(redirect) == tty) {
> - f = redirect;
> - redirect = NULL;
> + redir = current->nsproxy->pid_ns->redirect;
> + if (redir && file_tty(redir) == tty) {
> + f = redir;
> + current->nsproxy->pid_ns->redirect = NULL;
> }
> spin_unlock(&redirect_lock);
>
> @@ -1163,10 +1168,12 @@ ssize_t redirected_tty_write(struct file *file, const char __user *buf,
> size_t count, loff_t *ppos)
> {
> struct file *p = NULL;
> + struct file *redir;
>
> spin_lock(&redirect_lock);
> - if (redirect)
> - p = get_file(redirect);
> + redir = current->nsproxy->pid_ns->redirect;
> + if (redir)
> + p = get_file(redir);
> spin_unlock(&redirect_lock);
>
> if (p) {
> @@ -2247,19 +2254,19 @@ static int tioccons(struct file *file)
> if (file->f_op->write == redirected_tty_write) {
> struct file *f;
> spin_lock(&redirect_lock);
> - f = redirect;
> - redirect = NULL;
> + f = current->nsproxy->pid_ns->redirect;
> + current->nsproxy->pid_ns->redirect = NULL;
> spin_unlock(&redirect_lock);
> if (f)
> fput(f);
> return 0;
> }
> spin_lock(&redirect_lock);
> - if (redirect) {
> + if (current->nsproxy->pid_ns->redirect) {
> spin_unlock(&redirect_lock);
> return -EBUSY;
> }
> - redirect = get_file(file);
> + current->nsproxy->pid_ns->redirect = get_file(file);
> spin_unlock(&redirect_lock);
> return 0;
> }
> diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
> index 215e5e3..b04870f 100644
> --- a/include/linux/pid_namespace.h
> +++ b/include/linux/pid_namespace.h
> @@ -38,6 +38,7 @@ struct pid_namespace {
> int hide_pid;
> int reboot; /* group exit code if this pidns was rebooted */
> unsigned int proc_inum;
> + struct file *redirect;
> };
>
> extern struct pid_namespace init_pid_ns;
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index c1c3dc1..af1bfce 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -18,6 +18,7 @@
> #include <linux/proc_fs.h>
> #include <linux/reboot.h>
> #include <linux/export.h>
> +#include <linux/file.h>
>
> #define BITS_PER_PAGE (PAGE_SIZE*8)
>
> @@ -138,6 +139,8 @@ static void destroy_pid_namespace(struct pid_namespace *ns)
> {
> int i;
>
> + if (ns->redirect)
> + fput(ns->redirect);
> proc_free_inum(ns->proc_inum);
> for (i = 0; i < PIDMAP_ENTRIES; i++)
> kfree(ns->pidmap[i].page);
--
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