su: Use termios ioctls to turn off echoing and read a password

apps/su.cpp

@@ -1,16 +1,63 @@
+#include <bits/termios.h>
 #include <os/ArgumentParser.h>
 #include <pwd.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <sys/ioctl.h>
 #include <unistd.h>
 
+static struct termios orig;
+
+void restore_terminal()
+{
+    ioctl(fileno(stdin), TCSETS, &orig);
+}
+
+char* getpass()
+{
+    fputs("Password: ", stdout);
+
+    if (ioctl(fileno(stdin), TCGETS, &orig) < 0)
+    {
+        perror("ioctl(TCGETS)");
+        return nullptr;
+    }
+
+    atexit(restore_terminal);
+
+    struct termios tc = orig;
+    tc.c_lflag &= ~ECHO;
+    if (ioctl(fileno(stdin), TCSETS, &tc) < 0)
+    {
+        perror("ioctl(TCSETS)");
+        return nullptr;
+    }
+
+    static char buf[1024];
+    char* rc = fgets(buf, sizeof(buf), stdin);
+
+    restore_terminal();
+    putchar('\n');
+
+    if (!rc)
+    {
+        perror("fgets");
+        return nullptr;
+    }
+
+    char* newline = strrchr(rc, '\n');
+    if (newline) *newline = 0;
+
+    return buf;
+}
+
 int main(int argc, char** argv)
 {
     StringView name;
 
     if (geteuid() != 0)
     {
-        fprintf(stderr, "su must be run as root!\n");
+        fprintf(stderr, "su must be setuid root!\n");
         return 1;
     }
 
@@ -25,12 +72,20 @@ int main(int argc, char** argv)
         return 1;
     }
 
-    if (getuid() != geteuid())
+    if (getuid() != geteuid() && *entry->pw_passwd)
     {
-        fprintf(stderr, "FIXME: you have to enter %s's password first!\n", name.chars());
+        char* pass = getpass();
+        if (!pass) return 1;
+
+        if (strcmp(pass, entry->pw_passwd))
+        {
+            fprintf(stderr, "Wrong password!\n");
             return 1;
         }
 
+        memset(pass, 0, strlen(pass));
+    }
+
     setgid(entry->pw_gid);
     setuid(entry->pw_uid);