Quoting Matt Brown (matt@xxxxxxxxx): > 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) ? 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. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
