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/defs.h

@@ -180,6 +180,10 @@ void            mountinit(void);
 // 1 if the filesystem on this device refuses writes -- a mounted snapshot.
 // Ask before mutating, not after: the create path panics on a failed dirlink.
 int             fs_readonly(uint dev);
+int             in_group(uint gid, int real);
+uint            inode_mode_bits(struct inode *ip);
+int             inode_permission(struct inode *ip, int mask, int real);
+int             capable(void);
 int             mount_add(uint dev, uint64 inum, uint fsdev, uint64 root,
                     const char *path, const char *source, const char *type);
 // Walk the mount table for /proc/mounts. `path` and `source` need MAXPATH
@@ -601,6 +605,8 @@ int             fork(void);
 int             growproc(int64);
 int             kill(int);
 int             sigsend_pgrp(int pgid, int sig);
+int             sigsend_user(int pid, int sig);
+int             sigsend_pgrp_user(int pgid, int sig);
 int             proc_pgid(int pid);
 int             proc_setpgid(int pid, int pgid);
 int             proc_setsid(void);

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,

include/dev/pty.h

@@ -39,3 +39,4 @@ void pts_close(struct inode*);
 
 // From kernel/fs/devfs.c: the inode of master N.
 struct inode *devfs_pty_master(int n);
+void devfs_pty_claim(int n, uint uid);

include/fs/file.h

@@ -134,6 +134,9 @@ struct inode {
   // that does not, in which case stat makes some up from the type. Bit 18 set
   // alone means a mode of 0000, which chmod can ask for.
   uint mode;
+  // Owner. Whatever the filesystem keeps: SchFS has stored them all along,
+  // FAT and the synthetic filesystems report root.
+  uint uid, gid;
   uint supermode;
   uint showmode;
   uint atime;