Pass any username by env variable

fakeid

@@ -1,3 +1,5 @@
 #!/bin/bash
 
+USER="$1"
+shift
 LD_PRELOAD=$(dirname "$(readlink -f "$0")")/fakeid.so "$@"

fakeid.c

@@ -1,20 +1,19 @@
 #define _GNU_SOURCE
 
+#include <stdlib.h>
 #include <dlfcn.h>
 #include <string.h>
 #include <sys/types.h>
 #include <pwd.h>
 
-char *username = "alice";
-
 int getlogin_r(char *buf, size_t bufsize) {
-    strncpy(buf, username, bufsize);
+    strncpy(buf, getenv("USER"), bufsize);
     return 0;
 }
 
 struct passwd *getpwuid(uid_t uid) {
     struct passwd *(*getpwuid)(uid_t) = dlsym(RTLD_NEXT, "getpwuid");
     struct passwd *pass = getpwuid(uid);
-    pass->pw_name = username;
+    pass->pw_name = getenv("USER");
     return pass;
 }