Qualify hosted development and compose service ownership

restricted-execution/default.nix

@@ -20,17 +20,9 @@ let
     runtime = nativeProbe;
     executable = "${nativeProbe}/bin/probe";
   };
-  identityLauncher =
+  mkIdentityLauncher =
-    pkgs.runCommand "quixos-restricted-identity-launcher"
+    settings: import ./identity-launcher.nix ({ inherit pkgs sandbox; } // settings);
-      {
+  identityLauncher = mkIdentityLauncher { };
-        nativeBuildInputs = [ pkgs.stdenv.cc ];
-      }
-      ''
-        mkdir -p "$out/bin"
-        $CC -O2 -Wall -Wextra -Werror ${./identity-launcher.c} \
-          -DSANDBOX_EXECUTABLE='"${sandbox}/bin/quixos-restricted-sandbox"' \
-          -o "$out/bin/quixos-restricted-engine"
-      '';
   # Transaction-port/value adapters do not need the browser's CRDT/Wasm engine.
   # Keep this surface explicit; it is bundled into checked restricted handlers.
   sdk = pkgs.runCommand "quixos-restricted-sdk" { nativeBuildInputs = [ pkgs.esbuild ]; } ''
@@ -73,6 +65,7 @@ in
     workerd
     sandbox
     identityLauncher
+    mkIdentityLauncher
     nativeProbeSandbox
     sdk
     runtime

restricted-execution/identity-launcher.c

@@ -20,17 +20,17 @@ static void fail(const char *message) {
 }
 
 int main(int argc, char **argv) {
-  const char *root = "/run/quixos-restricted-engines/";
+  const char *root = ENGINE_DIRECTORY "/";
   uid_t caller = getuid();
   gid_t group = getgid();
-  struct passwd *owner = getpwnam("quixos-graph");
+  struct passwd *owner = getpwnam(AUTHORITY_USER);
   if (geteuid() != 0) fail("privileged wrapper unavailable");
   if (!owner) fail("authority identity unavailable");
   if (caller != owner->pw_uid) fail("caller identity mismatch");
   if (argc != 3) fail("invalid arguments");
   char *end;
   unsigned long number = strtoul(argv[2], &end, 10);
-  if (!*argv[2] || *end || number < 610000 || number >= 610064)
+  if (!*argv[2] || *end || number < ENGINE_FIRST_UID || number >= ENGINE_FIRST_UID + ENGINE_IDENTITY_COUNT)
     fail("invalid engine identity");
   uid_t identity = (uid_t)number;
   if (strlen(argv[1]) != strlen(root) + 16 || strncmp(argv[1], root, strlen(root)))
@@ -39,7 +39,7 @@ int main(int argc, char **argv) {
   if (strncmp(name, "qx-engine-", 10) ||
       strlen(name) != 16 || strspn(name + 10, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789") != 6)
     fail("invalid engine directory");
-  int parent = open("/run/quixos-restricted-engines", O_RDONLY | O_DIRECTORY | O_NOFOLLOW);
+  int parent = open(ENGINE_DIRECTORY, O_RDONLY | O_DIRECTORY | O_NOFOLLOW);
   struct stat info;
   if (parent < 0 || fstat(parent, &info) || info.st_uid != caller || (info.st_mode & 066))
     fail("invalid engine root");

restricted-execution/identity-launcher.nix

@@ -0,0 +1,28 @@
+# Trusted host construction only. Authored Workers cannot choose the caller,
+# reserved identities, engine directory or sandbox executable.
+{
+  pkgs,
+  sandbox,
+  authorityUser ? "quixos-graph",
+  engineDirectory ? "/run/quixos-restricted-engines",
+  firstUid ? 610000,
+  identityCount ? 64,
+}:
+assert builtins.match "[a-z][a-z0-9_-]{0,63}" authorityUser != null;
+assert builtins.match "/run/[a-zA-Z0-9_/-]+" engineDirectory != null;
+assert !(pkgs.lib.hasInfix ".." engineDirectory);
+assert !(pkgs.lib.hasSuffix "/" engineDirectory);
+assert builtins.stringLength engineDirectory < 80;
+assert builtins.isInt firstUid && builtins.isInt identityCount;
+assert firstUid >= 610000 && firstUid + identityCount <= 2147483647;
+assert identityCount >= 1 && identityCount <= 64;
+pkgs.runCommand "quixos-restricted-identity-launcher" { nativeBuildInputs = [ pkgs.stdenv.cc ]; } ''
+  mkdir -p "$out/bin"
+  $CC -O2 -Wall -Wextra -Werror ${./identity-launcher.c} \
+    -DSANDBOX_EXECUTABLE='"${sandbox}/bin/quixos-restricted-sandbox"' \
+    -DAUTHORITY_USER='"${authorityUser}"' \
+    -DENGINE_DIRECTORY='"${engineDirectory}"' \
+    -DENGINE_FIRST_UID=${toString firstUid} \
+    -DENGINE_IDENTITY_COUNT=${toString identityCount} \
+    -o "$out/bin/quixos-restricted-engine"
+''

restricted-execution/identity-module.nix

@@ -2,23 +2,45 @@
   executor,
   enable,
   controlGroup,
+  authorityUser ? "quixos-graph",
+  engineDirectory ? "/run/quixos-restricted-engines",
+  firstUid ? 610000,
+  identityCount ? 64,
+  wrapperName ? "quixos-restricted-engine",
 }:
 { config, lib, ... }:
 {
   config = lib.mkIf enable {
     assertions = [
       {
-        assertion = lib.all (user: user.uid == null || user.uid < 610000 || user.uid >= 610064) (
+        assertion = lib.all (
-          builtins.attrValues config.users.users
+          user: user.uid == null || user.uid < firstUid || user.uid >= firstUid + identityCount
-        );
+        ) (builtins.attrValues config.users.users);
-        message = "UIDs 610000–610063 are reserved for restricted engine identities.";
+        message = "UIDs ${toString firstUid}–${
+          toString (firstUid + identityCount - 1)
+        } are reserved for restricted engine identities.";
+      }
+      {
+        assertion = lib.all (
+          group: group.gid == null || group.gid < firstUid || group.gid >= firstUid + identityCount
+        ) (builtins.attrValues config.users.groups);
+        message = "Restricted engine GIDs must not overlap host groups.";
       }
     ];
     systemd.tmpfiles.rules = [
-      "d /run/quixos-restricted-engines 0711 quixos-graph ${controlGroup} -"
+      "d ${engineDirectory} 0711 ${authorityUser} ${controlGroup} -"
     ];
-    security.wrappers.quixos-restricted-engine = {
+    security.wrappers.${wrapperName} = {
-      source = "${executor.identityLauncher}/bin/quixos-restricted-engine";
+      source = "${
+        executor.mkIdentityLauncher {
+          inherit
+            authorityUser
+            engineDirectory
+            firstUid
+            identityCount
+            ;
+        }
+      }/bin/quixos-restricted-engine";
       owner = "root";
       group = controlGroup;
       permissions = "u+rx,g+rx,o-rwx";