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>

4 files changed, 24 insertions, 16 deletions

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 9a65eeaf7dfa..77bdfa7f8428 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -717,16 +717,23 @@ static int apparmor_task_setrlimit(struct task_struct *task,
 }
 
 static int apparmor_task_kill(struct task_struct *target, struct siginfo *info,
-			      int sig, u32 secid)
+			      int sig, const struct cred *cred)
 {
 	struct aa_label *cl, *tl;
 	int error;
 
-	if (secid)
-		/* TODO: after secid to label mapping is done.
-		 *  Dealing with USB IO specific behavior
+	if (cred) {
+		/*
+		 * Dealing with USB IO specific behavior
 		 */
-		return 0;
+		cl = aa_get_newest_cred_label(cred);
+		tl = aa_get_task_label(target);
+		error = aa_may_signal(cl, tl, sig);
+		aa_put_label(cl);
+		aa_put_label(tl);
+		return error;
+	}
+
 	cl = __begin_current_label_crit_section();
 	tl = aa_get_task_label(target);
 	error = aa_may_signal(cl, tl, sig);
diff --git a/security/security.c b/security/security.c
index 1cd8526cb0b7..14c291910d25 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1114,9 +1114,9 @@ int security_task_movememory(struct task_struct *p)
 }
 
 int security_task_kill(struct task_struct *p, struct siginfo *info,
-			int sig, u32 secid)
+			int sig, const struct cred *cred)
 {
-	return call_int_hook(task_kill, 0, p, info, sig, secid);
+	return call_int_hook(task_kill, 0, p, info, sig, cred);
 }
 
 int security_task_prctl(int option, unsigned long arg2, unsigned long arg3,
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);
 }
 
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 03fdecba93bb..feada2665322 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -2228,15 +2228,13 @@ static int smack_task_movememory(struct task_struct *p)
  * @p: the task object
  * @info: unused
  * @sig: unused
- * @secid: identifies the smack to use in lieu of current's
+ * @cred: identifies the cred to use in lieu of current's
  *
  * Return 0 if write access is permitted
  *
- * The secid behavior is an artifact of an SELinux hack
- * in the USB code. Someday it may go away.
  */
 static int smack_task_kill(struct task_struct *p, struct siginfo *info,
-			   int sig, u32 secid)
+			   int sig, const struct cred *cred)
 {
 	struct smk_audit_info ad;
 	struct smack_known *skp;
@@ -2252,17 +2250,17 @@ static int smack_task_kill(struct task_struct *p, struct siginfo *info,
 	 * Sending a signal requires that the sender
 	 * can write the receiver.
 	 */
-	if (secid == 0) {
+	if (cred == NULL) {
 		rc = smk_curacc(tkp, MAY_DELIVER, &ad);
 		rc = smk_bu_task(p, MAY_DELIVER, rc);
 		return rc;
 	}
 	/*
-	 * If the secid isn't 0 we're dealing with some USB IO
+	 * If the cred isn't NULL we're dealing with some USB IO
 	 * specific behavior. This is not clean. For one thing
 	 * we can't take privilege into account.
 	 */
-	skp = smack_from_secid(secid);
+	skp = smk_of_task(cred->security);
 	rc = smk_access(skp, tkp, MAY_DELIVER, &ad);
 	rc = smk_bu_note("USB signal", skp, tkp, MAY_DELIVER, rc);
 	return rc;