kernel: Add fallback if user didn't implement 'get_cred_rcu'

tiann/KernelSU#2320

Signed-off-by: rsuntk <rissu.ntk@gmail.com>

drivers/kernelsu/core_hook.c

@@ -182,7 +182,7 @@ static void setup_groups(struct root_profile *profile, struct cred *cred)
 	set_groups(cred, group_info);
 }
 
-static void disable_seccomp()
+static void disable_seccomp(void)
 {
 	assert_spin_locked(&current->sighand->siglock);
 	// disable seccomp
@@ -204,6 +204,7 @@ void ksu_escape_to_root(void)
 {
 	struct cred *cred;
 
+#ifdef KSU_GET_CRED_RCU
 	rcu_read_lock();
 
 	do {
@@ -216,6 +217,15 @@ void ksu_escape_to_root(void)
 		rcu_read_unlock();
 		return;
 	}
+#else
+	cred = (struct cred *)__task_cred(current);
+
+	if (cred->euid.val == 0) {
+		pr_warn("Already root, don't escape!\n");
+		return;
+	}
+#endif
+
 	struct root_profile *profile = ksu_get_root_profile(cred->uid.val);
 
 	cred->uid.val = profile->uid;
@@ -252,8 +262,10 @@ void ksu_escape_to_root(void)
 			sizeof(cred->cap_ambient));
 
 	setup_groups(profile, cred);
-
+
+#ifdef KSU_GET_CRED_RCU
 	rcu_read_unlock();
+#endif
 
 	// Refer to kernel/seccomp.c: seccomp_set_mode_strict
 	// When disabling Seccomp, ensure that current->sighand->siglock is held during the operation.