accounts: Add /etc/subuid and /etc/subgid support.

This commit adds a new record type, <subid-entry> and serializers
and deserializers for it in (gnu build accounts).  Each instance of this
record represents one line in either /etc/subuid or /etc/subgid.  Since
Shadow uses the same representation for both files, it should be ok if
we do it as well.

This commit adds also <subid-range>, a user facing representation of
<subid-entry>. It is supposed to be usable directly in OS configurations.

* gnu/build/accounts.scm (subid-entry): New record;
(write-subgid): add serializer for subgids;
(write-subuid): add serializer for subuids;
(read-subgid): add serializer for subgids;
(read-subuid): add serializer for subuids.
* gnu/system/accounts.scm (subid-range): New record.
* test/accounts.scm: Test them.

Change-Id: I6b037e40e354c069bf556412bb5b626bd3ea1b2c
Signed-off-by: Giacomo Leidi <goodoldpaul@autistici.org>
Signed-off-by: Ludovic Courtès <ludo@gnu.org>

3 files changed, 106 insertions, 3 deletions

diff --git a/gnu/build/accounts.scm b/gnu/build/accounts.scm
index fa6f454b5ed..ea8c69f2051 100644
--- a/gnu/build/accounts.scm
+++ b/gnu/build/accounts.scm
@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2019, 2021, 2023 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2024 Giacomo Leidi <goodoldpaul@autistici.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -51,13 +52,23 @@
             group-entry-gid
             group-entry-members
 
+            subid-entry
+            subid-entry?
+            subid-entry-name
+            subid-entry-start
+            subid-entry-count
+
             %password-lock-file
             write-group
             write-passwd
             write-shadow
+            write-subgid
+            write-subuid
             read-group
             read-passwd
             read-shadow
+            read-subgid
+            read-subuid
 
             %id-min
             %id-max
@@ -68,11 +79,12 @@
 
 ;;; Commentary:
 ;;;
-;;; This modules provides functionality equivalent to the C library's
+;;; This module provides functionality equivalent to the C library's
 ;;; <shadow.h>, <pwd.h>, and <grp.h> routines, as well as a subset of the
 ;;; functionality of the Shadow command-line tools.  It can parse and write
-;;; /etc/passwd, /etc/shadow, and /etc/group.  It can also take care of UID
-;;; and GID allocation in a way similar to what 'useradd' does.
+;;; /etc/passwd, /etc/shadow, /etc/group, /etc/subuid and /etc/subgid.  It can
+;;; also take care of UID and GID allocation in a way similar to what 'useradd'
+;;; does.  The same goes for sub UID and sub GID allocation.
 ;;;
 ;;; The benefit is twofold: less code is involved, and the ID allocation
 ;;; strategy and state preservation is made explicit.
@@ -225,6 +237,17 @@ each field."
                    (serialization list->comma-separated comma-separated->list)
                    (default '())))
 
+(define-database-entry <subid-entry>              ;<subid.h>
+  subid-entry make-subid-entry
+  subid-entry?
+  (serialization #\: subid-entry->string string->subid-entry)
+
+  (name            subid-entry-name)
+  (start           subid-entry-start
+                   (serialization number->string string->number))
+  (count           subid-entry-count
+                   (serialization number->string string->number)))
+
 (define %password-lock-file
   ;; The password database lock file used by libc's 'lckpwdf'.  Users should
   ;; grab this lock with 'with-file-lock' when they access the databases.
@@ -265,6 +288,10 @@ to it atomically and set the appropriate permissions."
   (database-writer "/etc/shadow" #o600 shadow-entry->string))
 (define write-group
   (database-writer "/etc/group" #o644 group-entry->string))
+(define write-subuid
+  (database-writer "/etc/subuid" #o644 subid-entry->string))
+(define write-subgid
+  (database-writer "/etc/subgid" #o644 subid-entry->string))
 
 (define (database-reader file string->entry)
   (lambda* (#:optional (file-or-port file))
@@ -287,6 +314,10 @@ to it atomically and set the appropriate permissions."
   (database-reader "/etc/shadow" string->shadow-entry))
 (define read-group
   (database-reader "/etc/group" string->group-entry))
+(define read-subuid
+  (database-reader "/etc/subuid" string->subid-entry))
+(define read-subgid
+  (database-reader "/etc/subgid" string->subid-entry))
 
 
 ;;;
diff --git a/gnu/system/accounts.scm b/gnu/system/accounts.scm
index 586cff1842e..9a006c188db 100644
--- a/gnu/system/accounts.scm
+++ b/gnu/system/accounts.scm
@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2013, 2014, 2015, 2016, 2017, 2018, 2019 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2024 Giacomo Leidi <goodoldpaul@autistici.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -39,6 +40,12 @@
             user-group-id
             user-group-system?
 
+            subid-range
+            subid-range?
+            subid-range-name
+            subid-range-start
+            subid-range-count
+
             sexp->user-account
             sexp->user-group
 
@@ -85,6 +92,16 @@
   (system?        user-group-system?              ; Boolean
                   (default #f)))
 
+(define-record-type* <subid-range>
+  subid-range make-subid-range
+  subid-range?
+  (name           subid-range-name)
+  (start          subid-range-start (default #f))    ; number
+  (count          subid-range-count                  ; number
+                  ; from find_new_sub_gids.c and
+                  ; find_new_sub_uids.c
+                  (default 65536)))
+
 (define (default-home-directory account)
   "Return the default home directory for ACCOUNT."
   (string-append "/home/" (user-account-name account)))
diff --git a/tests/accounts.scm b/tests/accounts.scm
index 78136390bbf..4944c22f499 100644
--- a/tests/accounts.scm
+++ b/tests/accounts.scm
@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2019 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2024 Giacomo Leidi <goodoldpaul@autistici.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -41,6 +42,16 @@ root:" (crypt "secret" "$6$abc") ":17169::::::
 charlie:" (crypt "hey!" "$6$abc") ":17169::::::
 nobody:!:0::::::\n"))
 
+(define %subuid-sample
+  "\
+root:100000:300
+ada:100300:300\n")
+
+(define %subgid-sample
+  "\
+root:100000:600
+ada:100600:300\n")
+
 
 (test-begin "accounts")
 
@@ -135,6 +146,50 @@ nobody:!:0::::::\n"))
                       read-shadow)
                     port))))
 
+(test-equal "write-subuid"
+  %subuid-sample
+  (call-with-output-string
+    (lambda (port)
+      (write-subuid (list (subid-entry
+                           (name "root")
+                           (start 100000)
+                           (count 300))
+                          (subid-entry
+                           (name "ada")
+                           (start 100300)
+                           (count 300)))
+                    port))))
+
+(test-equal "read-subuid + write-subuid"
+  %subuid-sample
+  (call-with-output-string
+    (lambda (port)
+      (write-subuid (call-with-input-string %subuid-sample
+                      read-subuid)
+                    port))))
+
+(test-equal "write-subgid"
+  %subgid-sample
+  (call-with-output-string
+    (lambda (port)
+      (write-subgid (list (subid-entry
+                           (name "root")
+                           (start 100000)
+                           (count 600))
+                          (subid-entry
+                           (name "ada")
+                           (start 100600)
+                           (count 300)))
+                    port))))
+
+(test-equal "read-subgid + write-subgid"
+  %subgid-sample
+  (call-with-output-string
+    (lambda (port)
+      (write-subgid (call-with-input-string %subgid-sample
+                      read-subgid)
+                    port))))
+
 
 (define allocate-groups (@@ (gnu build accounts) allocate-groups))
 (define allocate-passwd (@@ (gnu build accounts) allocate-passwd))