usb, signal, security: only pass the cred, not the secid, to kill_pid_info_as_cred and security_task_kill

commit d178bc3a708f39cbfefc3fab37032d3f2511b4ec ("user namespace: usb:
 make usb urbs user namespace aware (v2)") changed kill_pid_info_as_uid
to kill_pid_info_as_cred, saving and passing a cred structure instead of
uids.  Since the secid can be obtained from the cred, drop the secid fields
from the usb_dev_state and async structures, and drop the secid argument to
kill_pid_info_as_cred.  Replace the secid argument to security_task_kill
with the cred.  Update SELinux, Smack, and AppArmor to use the cred, which
avoids the need for Smack and AppArmor to use a secid at all in this hook.
Further changes to Smack might still be required to take full advantage of
this change, since it should now be possible to perform capability
checking based on the supplied cred.  The changes to Smack and AppArmor
have only been compile-tested.

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: Paul Moore <paul@paul-moore.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: James Morris <james.morris@microsoft.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 8644d864e3c1..8abd542c6b7c 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -4036,16 +4036,19 @@ static int selinux_task_movememory(struct task_struct *p)
 }
 
 static int selinux_task_kill(struct task_struct *p, struct siginfo *info,
-                                int sig, u32 secid)
+                                int sig, const struct cred *cred)
 {
+        u32 secid;
         u32 perm;
 
         if (!sig)
                 perm = PROCESS__SIGNULL; /* null signal; existence test */
         else
                 perm = signal_to_av(sig);
-        if (!secid)
+        if (!cred)
                 secid = current_sid();
+        else
+                secid = cred_sid(cred);
         return avc_has_perm(secid, task_sid(p), SECCLASS_PROCESS, perm, NULL);
 }