kernel: try introduce like susfs's method to fix prctl delay

Co-authored-by: AlexLiuDev233 <wzylin11@outlook.com>

kernel/core_hook.c

@@ -471,6 +471,9 @@ int ksu_handle_prctl(int option, unsigned long arg2, unsigned long arg3,
 	u32 *result = (u32 *)arg5;
 	u32 reply_ok = KERNEL_SU_OPTION;
 	uid_t current_uid_val = current_uid().val;
+if (likely(ksu_is_current_proc_umounted())) { // prevent side channel attack in ksu side
+		return 0;
+	}
 
 #ifdef CONFIG_KSU_MANUAL_SU
 	is_manual_su_cmd = (arg2 == CMD_SU_ESCALATION_REQUEST ||
@@ -1082,6 +1085,10 @@ int ksu_handle_setuid(struct cred *new, const struct cred *old)
 	// try umount ksu temp path
 	try_umount("/debug_ramdisk", false, MNT_DETACH);
 
+	get_task_struct(current); // delay fix
+	ksu_set_current_proc_umounted();
+	put_task_struct(current);
+
 	return 0;
 }
 

kernel/core_hook.h

@@ -3,8 +3,19 @@
 
 #include <linux/init.h>
 #include "apk_sign.h"
+#include <linux/thread_info.h>
 
 void __init ksu_core_init(void);
 void ksu_core_exit(void);
 
+#define KSU_PROC_UMOUNT 50
+
+static inline bool ksu_is_current_proc_umounted(void) {
+	return test_ti_thread_flag(&current->thread_info, KSU_PROC_UMOUNT);
+}
+
+static inline void ksu_set_current_proc_umounted(void) {
+	set_ti_thread_flag(&current->thread_info, KSU_PROC_UMOUNT);
+}
+
 #endif