[PATCH] image-account-extension: configure adduser UID/GID pools

["'Cedric Hombourger' via isar-users" <isar-users@googlegroups.com>]

For users and groups with an explicit uid/gid set, generate adduser pool
files so that maintainer scripts calling adduser/addgroup during package
installation will reserve the expected IDs.

A new 'reserve-only' flag allows entries to exist solely for pool
reservation without being explicitly created during image postprocessing.

Work-around: /etc/adduser.conf is pre-created with UID_POOL/GID_POOL
directives and --force-confold is passed to dpkg so that our version is
kept when the adduser package is installed. This is needed because
adduser does not support loading configuration fragments from a .d
directory or from environment variables. We want to discuss this!
Do we want to create images from a template richer than bootstrap
so adduser could be pre-installed and possibly its configuration
already patched to use UID_POOL / GID_POOL?

Signed-off-by: Cedric Hombourger <cedric.hombourger@siemens.com>
---
 doc/user_manual.md                            |  44 +++++--
 .../image-account-extension.bbclass           | 113 +++++++++++++++++-
 2 files changed, 145 insertions(+), 12 deletions(-)

diff --git a/doc/user_manual.md b/doc/user_manual.md
index 69e8dfef..3bd2e767 100644
--- a/doc/user_manual.md
+++ b/doc/user_manual.md
@@ -737,7 +737,8 @@ The `GROUP_<groupname>` variable contains the settings of a group named `groupna
 
  - `gid` - The numeric group id.
  - `flags` - A list of additional flags of the group. Those are the currently recognized flags:
-   - `system` - The group is created using the `--system` parameter.
+    - `system` - The group is created using the `--system` parameter.
+    - `reserve-only` - The group is not explicitly created during image postprocessing. Instead, its `gid` is reserved in the adduser GID pool so that packages creating this group via maintainer scripts will use the specified ID.
 
 The `USERS` and `USER:<username>` variable works similar to the `GROUPS` and `GROUP:<groupname>` variable. The difference are the accepted flags of the `USER:<username>` variable. It accepts the following flags:
 
@@ -750,13 +751,14 @@ The `USERS` and `USER:<username>` variable works similar to the `GROUPS` and `GR
  - `home` - This changes the default home directory of the user with `usermod --move-home`. Only takes effect when used together with the `create-home` flag.
  - `shell` - This users login shell
  - `groups` - A space separated list of groups this user is a member of.
- - `flags` - A list of additional flags of the user:
-   - `no-create-home` - `useradd` will be called with `-M` to prevent creation of the users home directory.
-   - `create-home` - `useradd` will be called with `-m` to force creation of the users home directory.
-   - `system` - `useradd` will be called with `--system`.
-   - `allow-empty-password` - Even if the `password` flag is empty, it will still be set. This results in a login without password.
-   - `clear-text-password` - The `password` flag of the given user contains a clear-text password and not an encrypted version of it.
-   - `force-passwd-change` - Force the user to change to password on first login.
+  - `flags` - A list of additional flags of the user:
+    - `no-create-home` - `useradd` will be called with `-M` to prevent creation of the users home directory.
+    - `create-home` - `useradd` will be called with `-m` to force creation of the users home directory.
+    - `system` - `useradd` will be called with `--system`.
+    - `allow-empty-password` - Even if the `password` flag is empty, it will still be set. This results in a login without password.
+    - `clear-text-password` - The `password` flag of the given user contains a clear-text password and not an encrypted version of it.
+    - `force-passwd-change` - Force the user to change to password on first login.
+    - `reserve-only` - The user is not explicitly created during image postprocessing. Instead, its `uid` is reserved in the adduser UID pool so that packages creating this user via maintainer scripts will use the specified ID.
 
 #### Example
 
@@ -779,6 +781,32 @@ USER_root[flags] = "create-home system force-passwd-change"
 
 Some examples can be also found in `meta-isar/conf/local.conf.sample`.
 
+#### UID/GID pool reservation
+
+When a user or group entry has an explicit `uid` or `gid` set, it is added to
+the adduser UID/GID pool. This ensures that packages creating users or groups
+via their maintainer scripts (e.g. `adduser` or `addgroup`) will allocate the
+specified IDs. Combined with the `reserve-only` flag, this allows reserving IDs
+without explicitly creating the accounts:
+
+```
+USERS += "tss"
+USER_tss[uid] = "666"
+USER_tss[flags] = "reserve-only"
+
+GROUPS += "tss"
+GROUP_tss[gid] = "666"
+GROUP_tss[flags] = "reserve-only"
+
+GROUPS += "docker"
+GROUP_docker[gid] = "1234"
+GROUP_docker[flags] = "reserve-only"
+```
+
+In this example, when `tpm2-abrmd` or `docker.io` are installed, their
+maintainer scripts will create the `tss` and `docker` accounts using the
+reserved IDs rather than dynamically allocated ones.
+
 #### Home directory contents prefilling
 
 To cover all users simply use `/etc/skel`. Files in there will be available in every home directory under correct permissions.
diff --git a/meta/classes-recipe/image-account-extension.bbclass b/meta/classes-recipe/image-account-extension.bbclass
index e874f3c7..7dfcd8e0 100644
--- a/meta/classes-recipe/image-account-extension.bbclass
+++ b/meta/classes-recipe/image-account-extension.bbclass
@@ -14,16 +14,18 @@ python() {
     for entry in (d.getVar("GROUPS") or "").split():
         group_entry = "GROUP_{}".format(entry)
         d.appendVarFlag("image_postprocess_accounts", "vardeps", " {}".format(group_entry))
+        d.appendVarFlag("image_configure_adduser_pools", "vardeps", " {}".format(group_entry))
         d.appendVarFlag("do_rootfs_install", "vardeps", " {}".format(group_entry))
 
     for entry in (d.getVar("USERS") or "").split():
         user_entry = "USER_{}".format(entry)
         d.appendVarFlag("image_postprocess_accounts", "vardeps", " {}".format(user_entry))
+        d.appendVarFlag("image_configure_adduser_pools", "vardeps", " {}".format(user_entry))
         d.appendVarFlag("do_rootfs_install", "vardeps", " {}".format(user_entry))
 }
 do_rootfs_install[vardeps] += "GROUPS USERS"
 
-def image_create_groups(d: "DataSmart") -> None:
+def image_create_groups(d):
     """Creates the groups defined in the ``GROUPS`` bitbake variable.
 
     Args:
@@ -40,6 +42,10 @@ def image_create_groups(d: "DataSmart") -> None:
         args = []
         group_entry = "GROUP_{}".format(entry)
 
+        flags = (d.getVarFlag(group_entry, "flags") or "").split()
+        if "reserve-only" in flags:
+            continue
+
         with open("{}/etc/group".format(rootfsdir), "r") as group_file:
             exists = any(line.startswith("{}:".format(entry)) for line in group_file)
 
@@ -59,7 +65,7 @@ def image_create_groups(d: "DataSmart") -> None:
             bb.process.run([*chroot, "/usr/sbin/groupadd", *args, entry])
 
 
-def image_create_users(d: "DataSmart") -> None:
+def image_create_users(d):
     """Creates the users defined in the ``USERS`` bitbake variable.
 
     Args:
@@ -78,6 +84,10 @@ def image_create_users(d: "DataSmart") -> None:
         args = []
         user_entry = "USER_{}".format(entry)
 
+        flags = (d.getVarFlag(user_entry, "flags") or "").split()
+        if "reserve-only" in flags:
+            continue
+
         with open("{}/etc/passwd".format(rootfsdir), "r") as passwd_file:
             exists = any(line.startswith("{}:".format(entry)) for line in passwd_file)
 
@@ -99,8 +109,6 @@ def image_create_users(d: "DataSmart") -> None:
             args.append("--groups")
             args.append(','.join(groups))
 
-        flags = (d.getVarFlag(user_entry, "flags") or "").split()
-
         if exists:
             add_user_option("--home", "home")
             if d.getVarFlag(user_entry, "home") or "":
@@ -143,6 +151,103 @@ def image_create_users(d: "DataSmart") -> None:
             bb.process.run([*chroot, "/usr/bin/passwd", "--expire", entry])
 
 
+def configure_adduser_pools(d):
+    """Configures adduser UID/GID pools for users and groups with explicit IDs.
+
+    Creates pool files and a minimal /etc/adduser.conf with UID_POOL/GID_POOL
+    directives before package installation.
+
+    Args:
+        d (DataSmart): The bitbake datastore.
+
+    Returns:
+        None
+    """
+    import os
+    import tempfile
+
+    rootfsdir = d.getVar("ROOTFSDIR")
+    adduser_conf = "{}/etc/adduser.conf".format(rootfsdir)
+    uid_pool_path = "/etc/adduser-uid.pool"
+    gid_pool_path = "/etc/adduser-gid.pool"
+
+    uid_pool_entries = []
+    seen_users = set()
+    for entry in (d.getVar("USERS") or "").split():
+        if entry in seen_users:
+            continue
+        seen_users.add(entry)
+        user_entry = "USER_{}".format(entry)
+        uid = d.getVarFlag(user_entry, "uid") or ""
+        if uid:
+            uid_pool_entries.append("{}:{}".format(entry, uid))
+
+    gid_pool_entries = []
+    seen_groups = set()
+    for entry in (d.getVar("GROUPS") or "").split():
+        if entry in seen_groups:
+            continue
+        seen_groups.add(entry)
+        group_entry = "GROUP_{}".format(entry)
+        gid = d.getVarFlag(group_entry, "gid") or ""
+        if gid:
+            gid_pool_entries.append("{}:{}".format(entry, gid))
+
+    if not uid_pool_entries and not gid_pool_entries:
+        return
+
+    if uid_pool_entries:
+        with tempfile.NamedTemporaryFile(mode="w", delete=False) as f:
+            f.write("\n".join(uid_pool_entries) + "\n")
+            tmp = f.name
+        bb.process.run(
+            ["sudo", "cp", tmp, "{}{}".format(rootfsdir, uid_pool_path)])
+        bb.process.run(
+            ["sudo", "chmod", "644", "{}{}".format(rootfsdir, uid_pool_path)])
+        os.unlink(tmp)
+
+    if gid_pool_entries:
+        with tempfile.NamedTemporaryFile(mode="w", delete=False) as f:
+            f.write("\n".join(gid_pool_entries) + "\n")
+            tmp = f.name
+        bb.process.run(
+            ["sudo", "cp", tmp, "{}{}".format(rootfsdir, gid_pool_path)])
+        bb.process.run(
+            ["sudo", "chmod", "644", "{}{}".format(rootfsdir, gid_pool_path)])
+        os.unlink(tmp)
+
+    # Create /etc/adduser.conf with the upstream default content plus pool
+    # directives. We use --force-confold during package installation so that
+    # dpkg keeps this version when the adduser package is installed.
+    conf_lines = []
+    conf_lines.append("# /etc/adduser.conf: `adduser' configuration.")
+    conf_lines.append("# See adduser(8) and adduser.conf(5) for full documentation.")
+    conf_lines.append("")
+    if uid_pool_entries:
+        conf_lines.append("UID_POOL={}".format(uid_pool_path))
+    if gid_pool_entries:
+        conf_lines.append("GID_POOL={}".format(gid_pool_path))
+
+    with tempfile.NamedTemporaryFile(mode="w", delete=False) as f:
+        f.write("\n".join(conf_lines) + "\n")
+        tmp = f.name
+    bb.process.run(["sudo", "cp", tmp, adduser_conf])
+    bb.process.run(["sudo", "chmod", "644", adduser_conf])
+    os.unlink(tmp)
+
+
+# Work-around: pre-create /etc/adduser.conf with pool directives and use
+# --force-confold so dpkg keeps our version when the adduser package is
+# installed. This is needed because adduser does not support loading
+# configuration from /etc/adduser.conf.d/ or from environment variables.
+ROOTFS_APT_ARGS += "-o DPkg::Options::=--force-confold"
+
+ROOTFS_CONFIGURE_COMMAND += "image_configure_adduser_pools"
+image_configure_adduser_pools[vardeps] += "USERS GROUPS"
+python image_configure_adduser_pools() {
+    configure_adduser_pools(d)
+}
+
 ROOTFS_POSTPROCESS_COMMAND += "image_postprocess_accounts"
 image_postprocess_accounts[vardeps] += "USERS GROUPS"
 python image_postprocess_accounts() {
-- 
2.47.3

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