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

include/core/proc.h

@@ -215,6 +215,8 @@ struct procinfo {
   int    nthreads;          // threads in that process
 };
 
+#define NGROUPS_MAX 32
+
 struct proc {
   uint64 sz;                   // Size of process memory (bytes)     [+0x00]
   pml4e_t* pgdir;              // Page table (PML4 on x86_64)        [+0x08]
@@ -335,6 +337,10 @@ struct proc {
   // are tracked honestly so getuid()/setuid() stop lying to userland.
   uint uid, euid, suid;
   uint gid, egid, sgid;
+  // Supplementary groups, as setgroups(2) set them: a file's group is
+  // consulted against these as well as against egid.
+  int  ngroups;
+  uint groups[NGROUPS_MAX];
 
   // --- Fair-share scheduling --------------------------------------------
   // The whole of the scheduler's per-process state. What each field means,