Only allow absolute paths

kernel/hal/hal.h

@@ -18,6 +18,7 @@ size_t hal_strcspn(const char *s, const char *reject);
 size_t hal_strspn(const char *s, const char *accept);
 char *hal_strcpy(char *dest, const char *src);
 char *hal_strchr(const char *s, int c);
+char *hal_strstr(const char *str, const char *substring);
 void hal_wait(uint32_t ms);
 int32_t hal_randnum(void);
 

kernel/hal/util.c

@@ -109,3 +109,34 @@ char *hal_strchr(const char *s, int c) {
     }
     return NULL;
 }
+
+char *hal_strstr(const char *str, const char *substring)
+{
+    const char *a;
+    const char *b;
+
+    b = substring;
+
+    if (*b == 0) {
+        return (char *) str;
+    }
+
+    for ( ; *str != 0; str += 1) {
+        if (*str != *b) {
+            continue;
+        }
+
+        a = str;
+        while (1) {
+            if (*b == 0) {
+                return (char *) str;
+            }
+            if (*a++ != *b++) {
+                break;
+            }
+        }
+        b = substring;
+    }
+
+    return NULL;
+}