Merge branch 'fixes-v5.0-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security

Pull security subsystem fixes from James Morris:
 "Fixes for the security subsystem.

  The first (by Casey actually - it's misattributed) fixes a regression
  introduced with the LSM stacking changes"

* 'fixes-v5.0-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security:
  LSM: Check for NULL cred-security on free
  Yama: Check for pid death before checking ancestry
  seccomp: fix UAF in user-trap code

kernel/seccomp.c

@@ -976,6 +976,9 @@ static int seccomp_notify_release(struct inode *inode, struct file *file)
 	struct seccomp_filter *filter = file->private_data;
 	struct seccomp_knotif *knotif;
 
+	if (!filter)
+		return 0;
+
 	mutex_lock(&filter->notify_lock);
 
 	/*
@@ -1300,6 +1303,7 @@ out:
 out_put_fd:
 	if (flags & SECCOMP_FILTER_FLAG_NEW_LISTENER) {
 		if (ret < 0) {
+			listener_f->private_data = NULL;
 			fput(listener_f);
 			put_unused_fd(listener);
 		} else {

security/security.c

@@ -1027,6 +1027,13 @@ int security_cred_alloc_blank(struct cred *cred, gfp_t gfp)
 
 void security_cred_free(struct cred *cred)
 {
+	/*
+	 * There is a failure case in prepare_creds() that
+	 * may result in a call here with ->security being NULL.
+	 */
+	if (unlikely(cred->security == NULL))
+		return;
+
 	call_void_hook(cred_free, cred);
 }
 

security/yama/yama_lsm.c

@@ -368,7 +368,9 @@ static int yama_ptrace_access_check(struct task_struct *child,
 			break;
 		case YAMA_SCOPE_RELATIONAL:
 			rcu_read_lock();
-			if (!task_is_descendant(current, child) &&
+			if (!pid_alive(child))
+				rc = -EPERM;
+			if (!rc && !task_is_descendant(current, child) &&
 			    !ptracer_exception_found(current, child) &&
 			    !ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
 				rc = -EPERM;