Messages in this thread | | | Subject | Re: [PATCH v3 1/2] tiocsti-restrict : Add owner user namespace to tty_struct | From | Matt Brown <> | Date | Sun, 23 Apr 2017 23:31:57 -0400 |
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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
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