Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1629093 > unrolled thread

[PATCH v3 1/2] tiocsti-restrict : Add owner user namespace to tty_struct

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  [PATCH v3 1/2] tiocsti-restrict : Add owner user namespace to tty_struct Matt Brown <matt@nmatt.com> - 2017-04-24 02:00 +0200
    Re: [PATCH v3 1/2] tiocsti-restrict : Add owner user namespace to  tty_struct "Serge E. Hallyn" <serge@hallyn.com> - 2017-04-24 03:20 +0200
      Re: [PATCH v3 1/2] tiocsti-restrict : Add owner user namespace to  tty_struct Matt Brown <matt@nmatt.com> - 2017-04-24 05:40 +0200
        Re: [PATCH v3 1/2] tiocsti-restrict : Add owner user namespace to  tty_struct "Serge E. Hallyn" <serge@hallyn.com> - 2017-04-24 05:50 +0200

#1629093 — [PATCH v3 1/2] tiocsti-restrict : Add owner user namespace to tty_struct

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@nmatt.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);
 
 	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

[toc] | [next] | [standalone]

#1629113 — Re: [PATCH v3 1/2] tiocsti-restrict : Add owner user namespace to tty_struct

Quoting Matt Brown (matt@nmatt.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@nmatt.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

[toc] | [prev] | [next] | [standalone]

#1629145 — Re: [PATCH v3 1/2] tiocsti-restrict : Add owner user namespace to tty_struct

On 04/23/2017 09:09 PM, Serge E. Hallyn wrote:
> Quoting Matt Brown (matt@nmatt.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@nmatt.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());
>

Does this mean I need to also use put_user_ns(tty->owner_user_ns) in
free_tty_struct instead of atomic_dec(&tty->owner_user_ns->count) ?

>>
>>  	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

[toc] | [prev] | [next] | [standalone]

#1629148 — Re: [PATCH v3 1/2] tiocsti-restrict : Add owner user namespace to tty_struct

Quoting Matt Brown (matt@nmatt.com):
> On 04/23/2017 09:09 PM, Serge E. Hallyn wrote:
> >Quoting Matt Brown (matt@nmatt.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@nmatt.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());
> >
> 
> Does this mean I need to also use put_user_ns(tty->owner_user_ns) in
> free_tty_struct instead of atomic_dec(&tty->owner_user_ns->count) ?

Yes, and since in theory the tty could outlive all the tasks in the
user namespace it needs to be put_user_ns() anyway so as to free it
on last put.

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web