Fix difference between PGID and GID. Correctly set UID and GID of new processes. Implement set/get PGID and GID.

programs/login.c

@@ -183,6 +183,9 @@ int main(int argc, char **argv)
         return 1;
     }
 
+    setgid(pwd->pw_gid);
+    setuid(pwd->pw_uid);
+
     char *_argv[] = { pwd->pw_shell, (char *)NULL };
     if (execv(pwd->pw_shell, _argv) == -1) {
         printf("%s: Failed to execute the shell.\n", argv[0]);

programs/mkdir.c

@@ -5,6 +5,7 @@
 /// See LICENSE.md for details.
 
 #include <stdio.h>
+#include <fcntl.h>
 #include <string.h>
 #include <sys/stat.h>
 #include <strerror.h>
@@ -23,7 +24,7 @@ int main(int argc, char *argv[])
         printf("    %s <directory>\n", argv[0]);
         return 0;
     }
-    if (mkdir(argv[1], 0)) {
+    if (mkdir(argv[1], S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH)) {
         printf("%s: cannot create directory '%s': %s\n", argv[0], argv[1], strerror(errno));
     }
     return 0;

programs/shell.c

@@ -747,7 +747,7 @@ int main(int argc, char *argv[])
             if (cpid == 0) {
                 // Makes the new process a group leader
                 pid_t pid = getpid();
-                setgid(pid);
+                setpgid(cpid, pid);
 
                 if (execvp(_argv[0], _argv) == -1) {
                     printf("\nUnknown command: %s\n", _argv[0]);

programs/touch.c

@@ -27,7 +27,7 @@ int main(int argc, char** argv)
     }
     int fd = open(argv[1], O_RDONLY, 0);
     if (fd < 0) {
-        fd = open(argv[1], O_CREAT, 0);
+        fd = open(argv[1], O_CREAT, S_IWUSR | S_IRUSR | S_IRGRP | S_IROTH);
         if (fd >= 0) {
             close(fd);
         }