user-classification: add new "foreign" UID range

This makes the UID range configurable via build time options, but of
course it really shouldn't be changed. The default range I picked is
outside even of IPAs current (ridiculously large) allocation ranges,
hence hopefully minimizes conflicts.

12 files changed, 78 insertions, 28 deletions

diff --git a/docs/UIDS-GIDS.md b/docs/UIDS-GIDS.md
index 09488e2a78..35018b77a4 100644
--- a/docs/UIDS-GIDS.md
+++ b/docs/UIDS-GIDS.md
@@ -129,10 +129,18 @@ possible.
    erroneously considers UIDs signed integers, and hence can't deal with values above 2^31.
    The `systemd-machined.service` service will synthesize user database records for all UIDs assigned to a running container from this range.
 
-Note for both allocation ranges: when a UID allocation takes place NSS is
-checked for collisions first, and a different UID is picked if an entry is found.
-Thus, the user database is used as synchronization mechanism to ensure
-exclusive ownership of UIDs and UID ranges.
+4. 2147352576…2147418111 → UID range used for foreign OS images. For various
+   usecases (primarily: containers) it makes sense to make foreign OS images
+   available locally whose UID/GID ownerships do not make sense in the local
+   context but only within the OS image itself. This 64K UID range can be used
+   to have a clearly defined ownership even on the host, that can be mapped via
+   idmapped mount to a dynamic runtime UID range as needed. (These numbers in
+   hexadecimal are 0x7FFE0000…0x7FFEFFFF.)
+
+Note for the `DynamicUser=` and the `systemd-nspawn` allocation ranges: when a
+UID allocation takes place NSS is checked for collisions first, and a different
+UID is picked if an entry is found.  Thus, the user database is used as
+synchronization mechanism to ensure exclusive ownership of UIDs and UID ranges.
 To ensure compatibility with other subsystems allocating from the same ranges it is hence essential that they
 ensure that whatever they pick shows up in the user/group databases, either by
 providing an NSS module, or by adding entries directly to `/etc/passwd` and `/etc/group`.
@@ -157,6 +165,8 @@ $ pkg-config --variable=container_uid_base_min systemd
 524288
 $ pkg-config --variable=container_uid_base_max systemd
 1878982656
+$ pkg-config --variable=foreign_uid_base systemd
+2147352576
 ```
 
 (Note that the latter encodes the maximum UID *base* `systemd-nspawn` might
@@ -164,7 +174,7 @@ pick — given that 64K UIDs are assigned to each container according to this
 allocation logic, the maximum UID used for this range is hence
 1878982656+65535=1879048191.)
 
-Systemd has compile-time default for these boundaries.
+systemd has compile-time default for these boundaries.
 Using those defaults is recommended.
 It will nevertheless query `/etc/login.defs` at runtime, when compiled with `-Dcompat-mutable-uid-boundaries=true` and that file is present.
 Support for this is considered only a compatibility feature and should not be
@@ -244,25 +254,27 @@ i.e. somewhere below `/var/` or similar.
 
 ## Summary
 
-|               UID/GID | Purpose               | Defined By    | Listed in                     |
-|-----------------------|-----------------------|---------------|-------------------------------|
-|                     0 | `root` user           | Linux         | `/etc/passwd` + `nss-systemd` |
-|                   1…4 | System users          | Distributions | `/etc/passwd`                 |
-|                     5 | `tty` group           | `systemd`     | `/etc/passwd`                 |
-|                 6…999 | System users          | Distributions | `/etc/passwd`                 |
-|            1000…60000 | Regular users         | Distributions | `/etc/passwd` + LDAP/NIS/…    |
-|           60001…60513 | Human users (homed)   | `systemd`     | `nss-systemd`                 |
-|           60514…60577 | Host users mapped into containers | `systemd` | `systemd-nspawn`      |
-|           60578…61183 | Unused                |               |                               |
-|           61184…65519 | Dynamic service users | `systemd`     | `nss-systemd`                 |
-|           65520…65533 | Unused                |               |                               |
-|                 65534 | `nobody` user         | Linux         | `/etc/passwd` + `nss-systemd` |
-|                 65535 | 16-bit `(uid_t) -1`   | Linux         |                               |
-|          65536…524287 | Unused                |               |                               |
-|     524288…1879048191 | Container UID ranges  | `systemd`     | `nss-systemd`                 |
-| 1879048192…2147483647 | Unused                |               |                               |
-| 2147483648…4294967294 | HIC SVNT LEONES       |               |                               |
-|            4294967295 | 32-bit `(uid_t) -1`   | Linux         |                               |
+|               UID/GID |   Same in Hexadecimal |   How Many | Purpose                           | Defined By    | Listed in                     |
+|----------------------:|----------------------:|-----------:|:----------------------------------|:--------------|:------------------------------|
+|                     0 |            0x00000000 |          1 | `root` user                       | Linux         | `/etc/passwd` + `nss-systemd` |
+|                   1…4 | 0x00000001…0x00000004 |          4 | System users                      | Distributions | `/etc/passwd`                 |
+|                     5 |            0x00000005 |          1 | `tty` group                       | `systemd`     | `/etc/passwd`                 |
+|                 6…999 | 0x00000006…0x000003E7 |        994 | System users                      | Distributions | `/etc/passwd`                 |
+|            1000…60000 | 0x000003E8…0x00001770 |      59000 | Regular users                     | Distributions | `/etc/passwd` + LDAP/NIS/…    |
+|           60001…60513 | 0x0000EA61…0x0000EC61 |        513 | Human users (homed)               | `systemd`     | `nss-systemd`                 |
+|           60514…60577 | 0x0000EC62…0x0000ECA1 |         64 | Host users mapped into containers | `systemd`     | `systemd-nspawn`              |
+|           60578…61183 | 0x0000ECA2…0x0000EEFF |        606 | *unused*                          |               |                               |
+|           61184…65519 | 0x0000EF00…0x0000FFEF |       4336 | Dynamic service users             | `systemd`     | `nss-systemd`                 |
+|           65520…65533 | 0x0000FFF0…0x0000FFFD |         13 | *unused*                          |               |                               |
+|                 65534 |            0x0000FFFE |          1 | `nobody` user                     | Linux         | `/etc/passwd` + `nss-systemd` |
+|                 65535 |            0x0000FFFF |          1 | 16-bit `(uid_t) -1`               | Linux         |                               |
+|          65536…524287 | 0x00010000…0x0007FFFF |     458752 | *unused*                          |               |                               |
+|     524288…1879048191 | 0x00080000…0x6FFFFFFF | 1878523904 | Container UID ranges              | `systemd`     | `nss-systemd`                 |
+| 1879048192…2147352575 | 0x70000000…0x7FFDFFFF | 1879048192 | *unused*                          |               |                               |
+| 2147352576…2147418111 | 0x7FFE0000…0x7FFEFFFF |      65536 | Foreign UID range                 | `systemd`     | `nss-systemd`                 |
+| 2147418112…2147483647 | 0x7FFF0000…0x7FFFFFFF |      65536 | *unused*                          |               |                               |
+| 2147483648…4294967294 | 0x80000000…0xFFFFFFFE | 2147483647 | *HIC SVNT LEONES*                 |               |                               |
+|            4294967295 |            0xFFFFFFFF |          1 | 32-bit `(uid_t) -1`               | Linux         |                               |
 
 Note that "Unused" in the table above doesn't mean that these ranges are really unused.
 It just means that these ranges have no well-established
diff --git a/docs/USER_RECORD.md b/docs/USER_RECORD.md
index 911fceb03f..1a219fed41 100644
--- a/docs/USER_RECORD.md
+++ b/docs/USER_RECORD.md
@@ -259,14 +259,17 @@ It's probably wise to use a location string processable by geo-location subsyste
 Example: `Berlin, Germany` or `Basement, Room 3a`.
 
 `disposition` → A string, one of `intrinsic`, `system`, `dynamic`, `regular`,
-`container`, `reserved`. If specified clarifies the disposition of the user,
+`container`, `foreign`, `reserved`. If specified clarifies the disposition of the user,
 i.e. the context it is defined in.
 For regular, "human" users this should be `regular`, for system users (i.e. users that system services run under, and similar) this should be `system`.
 The `intrinsic` disposition should be used only for the two users that have special meaning to the OS kernel itself,
 i.e. the `root` and `nobody` users.
 The `container` string should be used for users that are used by an OS container, and hence will show up in `ps` listings
 and such, but are only defined in container context.
-Finally `reserved` should be used for any users outside of these use-cases.
+The `foreign` string should be used for users from UID ranges which are used
+for OS images from foreign systems, i.e. where local resolution would not make
+sense.
+Finally, `reserved` should be used for any users outside of these use-cases.
 Note that this property is entirely optional and applications are assumed to be able to derive the
 disposition of a user automatically from a record even in absence of this
 field, based on other fields, for example the numeric UID. By setting this
diff --git a/meson.build b/meson.build
index af57c0969b..6a7e76371a 100644
--- a/meson.build
+++ b/meson.build
@@ -877,6 +877,9 @@ container_uid_base_max = get_option('container-uid-base-max')
 conf.set('CONTAINER_UID_BASE_MIN', container_uid_base_min)
 conf.set('CONTAINER_UID_BASE_MAX', container_uid_base_max)
 
+foreign_uid_base = get_option('foreign-uid-base')
+conf.set('FOREIGN_UID_BASE', foreign_uid_base)
+
 nobody_user = get_option('nobody-user')
 nobody_group = get_option('nobody-group')
 
@@ -2985,6 +2988,7 @@ summary({
                                                                          conf.get('SYSTEM_ALLOC_GID_MIN')),
         'dynamic UIDs' :                    '@0@…@1@'.format(dynamic_uid_min, dynamic_uid_max),
         'container UID bases' :             '@0@…@1@'.format(container_uid_base_min, container_uid_base_max),
+        'foreign UID base' :                '@0@'.format(foreign_uid_base),
         'static UID/GID allocations' :      ' '.join(static_ugids),
         '/dev/kvm access mode' :            get_option('dev-kvm-mode'),
         'render group access mode' :        get_option('group-render-mode'),
diff --git a/meson_options.txt b/meson_options.txt
index d9242d3b30..edf8053e51 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -273,6 +273,8 @@ option('container-uid-base-min', type : 'integer', value : 0x00080000,
        description : 'minimum container UID base')
 option('container-uid-base-max', type : 'integer', value : 0x6FFF0000,
        description : 'maximum container UID base')
+option('foreign-uid-base', type : 'integer', value : 0x7FFE0000,
+       description : 'foreign OS image UID base')
 option('adm-group', type : 'boolean',
        description : 'the ACL for adm group should be added')
 option('wheel-group', type : 'boolean',
diff --git a/src/basic/uid-classification.c b/src/basic/uid-classification.c
index e2d2cebc6d..88be896ff4 100644
--- a/src/basic/uid-classification.c
+++ b/src/basic/uid-classification.c
@@ -127,5 +127,5 @@ bool uid_for_system_journal(uid_t uid) {
 
         /* Returns true if the specified UID shall get its data stored in the system journal. */
 
-        return uid_is_system(uid) || uid_is_dynamic(uid) || uid == UID_NOBODY || uid_is_container(uid);
+        return uid_is_system(uid) || uid_is_dynamic(uid) || uid == UID_NOBODY || uid_is_container(uid) || uid_is_foreign(uid);
 }
diff --git a/src/basic/uid-classification.h b/src/basic/uid-classification.h
index 0932123d5c..2d76be5f04 100644
--- a/src/basic/uid-classification.h
+++ b/src/basic/uid-classification.h
@@ -12,6 +12,10 @@ assert_cc((CONTAINER_UID_BASE_MAX & 0xFFFFU) == 0);
 #define CONTAINER_UID_MIN (CONTAINER_UID_BASE_MIN)
 #define CONTAINER_UID_MAX (CONTAINER_UID_BASE_MAX + 0xFFFFU)
 
+assert_cc((FOREIGN_UID_BASE & 0xFFFFU) == 0);
+#define FOREIGN_UID_MIN (FOREIGN_UID_BASE)
+#define FOREIGN_UID_MAX (FOREIGN_UID_BASE + 0xFFFFU)
+
 bool uid_is_system(uid_t uid);
 bool gid_is_system(gid_t gid);
 
@@ -31,6 +35,14 @@ static inline bool gid_is_container(gid_t gid) {
         return uid_is_container((uid_t) gid);
 }
 
+static inline bool uid_is_foreign(uid_t uid) {
+        return FOREIGN_UID_MIN <= uid && uid <= FOREIGN_UID_MAX;
+}
+
+static inline bool gid_is_foreign(gid_t gid) {
+        return uid_is_foreign((uid_t) gid);
+}
+
 typedef struct UGIDAllocationRange {
         uid_t system_alloc_uid_min;
         uid_t system_uid_max;
diff --git a/src/core/systemd.pc.in b/src/core/systemd.pc.in
index f3b85b0190..8d044dd7ad 100644
--- a/src/core/systemd.pc.in
+++ b/src/core/systemd.pc.in
@@ -102,6 +102,8 @@ containeruidbasemin=${container_uid_base_min}
 container_uid_base_max={{CONTAINER_UID_BASE_MAX}}
 containeruidbasemax=${container_uid_base_max}
 
+foreign_uid_base={{FOREIGN_UID_BASE}}
+
 Name: systemd
 Description: systemd System and Service Manager
 URL: {{PROJECT_URL}}
diff --git a/src/dissect/dissect.c b/src/dissect/dissect.c
index 91f0f1de13..cb51d71384 100644
--- a/src/dissect/dissect.c
+++ b/src/dissect/dissect.c
@@ -1199,7 +1199,7 @@ static const char *pick_color_for_uid_gid(uid_t uid) {
                 return ansi_normal();            /* files in disk images are typically owned by root and other system users, no issue there */
         if (uid_is_dynamic(uid))
                 return ansi_highlight_red();     /* files should never be owned persistently by dynamic users, and there are just no excuses */
-        if (uid_is_container(uid))
+        if (uid_is_container(uid) || uid_is_foreign(uid))
                 return ansi_highlight_cyan();
 
         return ansi_highlight();
diff --git a/src/shared/group-record.c b/src/shared/group-record.c
index 4898616252..eea60af334 100644
--- a/src/shared/group-record.c
+++ b/src/shared/group-record.c
@@ -303,6 +303,9 @@ UserDisposition group_record_disposition(GroupRecord *h) {
         if (gid_is_container(h->gid))
                 return USER_CONTAINER;
 
+        if (gid_is_foreign(h->gid))
+                return USER_FOREIGN;
+
         if (h->gid > INT32_MAX)
                 return USER_RESERVED;
 
diff --git a/src/shared/user-record.c b/src/shared/user-record.c
index 131949a4e4..88970425cc 100644
--- a/src/shared/user-record.c
+++ b/src/shared/user-record.c
@@ -1993,6 +1993,9 @@ UserDisposition user_record_disposition(UserRecord *h) {
         if (uid_is_container(h->uid))
                 return USER_CONTAINER;
 
+        if (uid_is_foreign(h->uid))
+                return USER_FOREIGN;
+
         if (h->uid > INT32_MAX)
                 return USER_RESERVED;
 
@@ -2712,6 +2715,7 @@ static const char* const user_disposition_table[_USER_DISPOSITION_MAX] = {
         [USER_DYNAMIC]   = "dynamic",
         [USER_REGULAR]   = "regular",
         [USER_CONTAINER] = "container",
+        [USER_FOREIGN]   = "foreign",
         [USER_RESERVED]  = "reserved",
 };
 
diff --git a/src/shared/user-record.h b/src/shared/user-record.h
index b539b3f55e..d3decdb5c1 100644
--- a/src/shared/user-record.h
+++ b/src/shared/user-record.h
@@ -17,6 +17,7 @@ typedef enum UserDisposition {
         USER_DYNAMIC,     /* dynamically allocated users for system services */
         USER_REGULAR,     /* regular (typically human users) */
         USER_CONTAINER,   /* UID ranges allocated for container uses */
+        USER_FOREIGN,     /* UID range allocated for foreign OS images */
         USER_RESERVED,    /* Range above 2^31 */
         _USER_DISPOSITION_MAX,
         _USER_DISPOSITION_INVALID = -EINVAL,
diff --git a/src/userdb/userdbctl.c b/src/userdb/userdbctl.c
index a803df8b0b..5a0359dccf 100644
--- a/src/userdb/userdbctl.c
+++ b/src/userdb/userdbctl.c
@@ -61,6 +61,7 @@ static const char *user_disposition_to_color(UserDisposition d) {
                 return ansi_green();
 
         case USER_CONTAINER:
+        case USER_FOREIGN:
                 return ansi_cyan();
 
         case USER_RESERVED:
@@ -170,6 +171,12 @@ static const struct {
                 .name = "container",
                 .disposition = USER_CONTAINER,
         },
+        {
+                .first = FOREIGN_UID_MIN,
+                .last = FOREIGN_UID_MAX,
+                .name = "foreign",
+                .disposition = USER_FOREIGN,
+        },
 #if ENABLE_HOMED
         {
                 .first = HOME_UID_MIN,