Users and permissions: accounts, login, enforced file permissions, setuid, su, passwd, doas

The kernel now checks owner/group/other on open, create, unlink, rename, exec
and path search; honours set-user-id and set-group-id; restricts kill, mount,
reboot and mknod; keeps supplementary groups; and implements chown. devtmpfs
nodes carry owners and modes that chmod/chown keep. Terminals run login, the
image has root and schos, X starts as the ordinary user.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EVRhxi9zpdW2uDUN4FVcao

kernel/dev/pty.c

@@ -144,6 +144,7 @@ ptmx_open(struct inode *ip)
     ptys[n].used = 0;
     return 0;
   }
+  devfs_pty_claim(n, myproc() ? myproc()->euid : 0);
   iunlockput(ip);
   ilock(m);
   return m;