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