Add proper error handling

fakeid.c

@@ -1,10 +1,11 @@
 #define _GNU_SOURCE
 
-#include <stdlib.h>
 #include <dlfcn.h>
+#include <pwd.h>
+#include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include <sys/types.h>
-#include <pwd.h>
 
 int getlogin_r(char *buf, size_t bufsize) {
     strncpy(buf, getenv("USER"), bufsize);
@@ -13,7 +14,16 @@ int getlogin_r(char *buf, size_t bufsize) {
 
 struct passwd *getpwuid(uid_t uid) {
     struct passwd *(*getpwuid)(uid_t) = dlsym(RTLD_NEXT, "getpwuid");
+    if (getpwuid == NULL) {
+        fprintf(stderr, "Unable to find the adress of the getpwuid function: %s\n", dlerror());
+        return NULL;
+    }
     struct passwd *pass = getpwuid(uid);
-    pass->pw_name = getenv("USER");
+    char *name = getenv("USER");
+    if (name == NULL) {
+        fprintf(stderr, "Could not find the USER environment variable. Using the real username.\n");
+        return pass;
+    }
+    pass->pw_name = name;
     return pass;
 }