On Fri, 2020-04-17 at 11:48 -0400, Paul Moore wrote:
> I just notice that the "selinux: Implement the watch_key security
> hook" patch made it's way into linux-next via 9ba09998baa9:
>
> commit 9ba09998baa995518d94c9a32e6329b28ccb9045
> Author: David Howells <dhowells@xxxxxxxxxx>
> Date: Tue Jan 14 17:07:13 2020 +0000
>
> selinux: Implement the watch_key security hook
>
> Implement the watch_key security hook to make sure that a key
> grants the
> caller View permission in order to set a watch on a key.
>
> For the moment, the watch_devices security hook is left
> unimplemented as
> it's not obvious what the object should be since the queue is
> global and
> didn't previously exist.
>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> Acked-by: Stephen Smalley <sds@xxxxxxxxxxxxx>
>
> I'm reasonably confident that this code hasn't been tested as I
> expect
> it would fail, or at the very least behave in unintended ways. The
> problem is the selinux_watch_key(...) function, shown below:
I built an selinx-testsuite test for this last year and it worked fine
then. I'll send the test as an RFC patch as its been some time since I
ran it. David also has a test in kernel
samples/watch_queue/watch_test.c
>
> +static int selinux_watch_key(struct key *key)
> +{
> + struct key_security_struct *ksec = key->security;
> + u32 sid = current_sid();
> +
> + return avc_has_perm(&selinux_state,
> + sid, ksec->sid, SECCLASS_KEY,
> KEY_NEED_VIEW, NULL);
> +}
>
> ... in particular it is the fifth argument to avc_has_perm(),
> "KEY_NEED_VIEW" which is a problem. KEY_NEED_VIEW is not a SELinux
True, however by magic the KEY_NEED_* perms match with the bits defined
in classmap.h. I did some work on this during the 'keys' saga, see
various emails in list like [1]
[1]
https://lore.kernel.org/selinux/20200220181031.156674-2-richard_c_haines@xxxxxxxxxxxxxx/
> permission and would likely result in odd behavior when passed to
> avc_has_perm(). Given that the keyring permission to SELinux object
> class permission is variable depending on the key_perms policy
> capability, it probably makes the most sense to pull the permission
> mapping in selinux_key_permission() out into a separate function,
> e.g.
> key_perm_to_av(...) (see the other XXX_to_av() functions in
> security/selinux/hooks.c), and then use this newly created mapping
> function in both selinux_key_permission() and
> selinux_watch_key(). Or
> you could just duplicate the KEY_NEED_VIEW mapping code in both
> functions, but I would advise against that.
>
