Smack: ptrace capability use fixes

This fixes a pair of problems in the Smack ptrace checks
related to checking capabilities. In both cases, as reported
by Lukasz Pawelczyk, the raw capability calls are used rather
than the Smack wrapper that check addition restrictions.
In one case, as reported by Jann Horn, the wrong task is being
checked for capabilities.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

security/smack/smack_lsm.c

@@ -421,6 +421,7 @@ static int smk_ptrace_rule_check(struct task_struct *tracer,
 	struct smk_audit_info ad, *saip = NULL;
 	struct task_smack *tsp;
 	struct smack_known *tracer_known;
+	const struct cred *tracercred;
 
 	if ((mode & PTRACE_MODE_NOAUDIT) == 0) {
 		smk_ad_init(&ad, func, LSM_AUDIT_DATA_TASK);
@@ -429,7 +430,8 @@ static int smk_ptrace_rule_check(struct task_struct *tracer,
 	}
 
 	rcu_read_lock();
-	tsp = __task_cred(tracer)->security;
+	tracercred = __task_cred(tracer);
+	tsp = tracercred->security;
 	tracer_known = smk_of_task(tsp);
 
 	if ((mode & PTRACE_MODE_ATTACH) &&
@@ -439,7 +441,7 @@ static int smk_ptrace_rule_check(struct task_struct *tracer,
 			rc = 0;
 		else if (smack_ptrace_rule == SMACK_PTRACE_DRACONIAN)
 			rc = -EACCES;
-		else if (capable(CAP_SYS_PTRACE))
+		else if (smack_privileged_cred(CAP_SYS_PTRACE, tracercred))
 			rc = 0;
 		else
 			rc = -EACCES;
@@ -1841,6 +1843,7 @@ static int smack_file_send_sigiotask(struct task_struct *tsk,
 {
 	struct smack_known *skp;
 	struct smack_known *tkp = smk_of_task(tsk->cred->security);
+	const struct cred *tcred;
 	struct file *file;
 	int rc;
 	struct smk_audit_info ad;
@@ -1854,8 +1857,12 @@ static int smack_file_send_sigiotask(struct task_struct *tsk,
 	skp = file->f_security;
 	rc = smk_access(skp, tkp, MAY_DELIVER, NULL);
 	rc = smk_bu_note("sigiotask", skp, tkp, MAY_DELIVER, rc);
-	if (rc != 0 && has_capability(tsk, CAP_MAC_OVERRIDE))
+
+	rcu_read_lock();
+	tcred = __task_cred(tsk);
+	if (rc != 0 && smack_privileged_cred(CAP_MAC_OVERRIDE, tcred))
 		rc = 0;
+	rcu_read_unlock();
 
 	smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_TASK);
 	smk_ad_setfield_u_tsk(&ad, tsk);