chroot: Add a little chroot program

This program changes the current filesystem root and spawns a shell.

Base/usr/share/man/man2/chroot.md

@@ -0,0 +1,26 @@
+## Name
+
+chroot - change filesystem root
+
+## Synopsis
+
+```**c++
+#include <unistd.h>
+
+int chroot(const char* path);
+```
+
+## Description
+
+`chroot()` changes the filesystem root of the current process to a new directory specified by `path`.
+
+## Errors
+
+* `EPERM`: The current process does not have superuser privileges.
+* `EFAULT`: `path` is not in readable memory.
+
+All of the usual path resolution errors may also occur.
+
+## See also
+
+* [`chroot`(8)](../man8/chroot.md)

Base/usr/share/man/man8/chroot.md

@@ -0,0 +1,28 @@
+## Name
+
+chroot - run a shell with a different filesystem root
+
+## Synopsis
+
+```**sh
+# chroot
+```
+
+## Description
+
+This program uses the [`chroot`(2)](../man2/chroot.md) syscall to switch into a
+different filesystem root and spawn a shell inside it.
+
+It will not work unless there is a `/bin/Shell` available inside the new root.
+
+## Examples
+
+```sh
+# chroot /var/chroot
+# pwd
+/
+```
+
+## See also
+
+* [`chroot`(2)](../man2/chroot.md)

Userland/chroot.cpp

@@ -0,0 +1,27 @@
+#include <stdio.h>
+#include <unistd.h>
+
+int main(int argc, char** argv)
+{
+    if (argc != 2) {
+        printf("usage: chroot <path>\n");
+        return 0;
+    }
+
+    if (chroot(argv[1]) < 0) {
+        perror("chroot");
+        return 1;
+    }
+
+    if (chdir("/") < 0) {
+        perror("chdir(/)");
+        return 1;
+    }
+
+    if (execl("/bin/Shell", "Shell", nullptr) < 0) {
+        perror("execl");
+        return 1;
+    }
+
+    return 0;
+}