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Message-ID: <20170424010941.GA32715@mail.hallyn.com>
Date: Sun, 23 Apr 2017 20:09:41 -0500
From: "Serge E. Hallyn" <serge@...lyn.com>
To: Matt Brown <matt@...tt.com>
Cc: serge@...lyn.com, jmorris@...ei.org, gregkh@...uxfoundation.org,
jslaby@...e.com, corbet@....net, keescook@...omium.org,
akpm@...ux-foundation.org, jannh@...gle.com,
kernel-hardening@...ts.openwall.com,
linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 1/2] tiocsti-restrict : Add owner user namespace to
tty_struct
Quoting Matt Brown (matt@...tt.com):
> This patch adds struct user_namespace *owner_user_ns to the tty_struct.
> Then it is set to current_user_ns() in the alloc_tty_struct function.
>
> This is done to facilitate capability checks against the original user
> namespace that allocated the tty.
>
> E.g. ns_capable(tty->owner_user_ns,CAP_SYS_ADMIN)
>
> This combined with the use of user namespace's will allow hardening
> protections to be built to mitigate container escapes that utilize TTY
> ioctls such as TIOCSTI.
>
> See: https://bugzilla.redhat.com/show_bug.cgi?id=1411256
>
> Signed-off-by: Matt Brown <matt@...tt.com>
> ---
> drivers/tty/tty_io.c | 4 ++++
> include/linux/tty.h | 2 ++
> 2 files changed, 6 insertions(+)
>
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index e6d1a65..03d5ea2 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -161,6 +161,7 @@ static void release_tty(struct tty_struct *tty, int idx);
> * @tty: tty struct to free
> *
> * Free the write buffers, tty queue and tty memory itself.
> + * Decrement the owner_user_ns count.
> *
> * Locking: none. Must be called after tty is definitely unused
> */
> @@ -171,6 +172,7 @@ static void free_tty_struct(struct tty_struct *tty)
> put_device(tty->dev);
> kfree(tty->write_buf);
> tty->magic = 0xDEADDEAD;
> + atomic_dec(&tty->owner_user_ns->count);
> kfree(tty);
> }
>
> @@ -3191,6 +3193,8 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx)
> tty->index = idx;
> tty_line_name(driver, idx, tty->name);
> tty->dev = tty_get_device(tty);
> + tty->owner_user_ns = current_user_ns();
> + atomic_inc(&tty->owner_user_ns->count);
Hi,
CONFIG_USER_NS is an option, so unfortunately you need to do
tty->owner_user_ns = get_user_ns(current_user_ns());
>
> return tty;
> }
> diff --git a/include/linux/tty.h b/include/linux/tty.h
> index 1017e904..d902d42 100644
> --- a/include/linux/tty.h
> +++ b/include/linux/tty.h
> @@ -12,6 +12,7 @@
> #include <uapi/linux/tty.h>
> #include <linux/rwsem.h>
> #include <linux/llist.h>
> +#include <linux/user_namespace.h>
>
>
> /*
> @@ -333,6 +334,7 @@ struct tty_struct {
> /* If the tty has a pending do_SAK, queue it here - akpm */
> struct work_struct SAK_work;
> struct tty_port *port;
> + struct user_namespace *owner_user_ns;
> };
>
> /* Each of a tty's open files has private_data pointing to tty_file_private */
> --
> 2.10.2
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