Merge pull request #100 from lucannez64/fix/host-dns

Use the host DNS resolver in Darling

.gitattributes

@@ -1,3 +1,3 @@
-# Unified-diff context uses a single space for an empty source line.
-# Do not report that patch syntax as trailing source whitespace.
-patches/*.patch whitespace=-blank-at-eol
+# Unified-diff context adds a space before source tabs and empty lines.
+# Do not report that patch syntax as source whitespace errors.
+patches/*.patch whitespace=-blank-at-eol,-space-before-tab

docs/TESTING.md

@@ -90,6 +90,19 @@ append-only output and tightening an existing public log to mode 0600. The
 runner test uses a fake `darling` executable to verify loopback fixtures and
 private-prefix-only shutdown/cleanup.
 
+With the pinned Darling sources available, run the host resolver regression:
+
+```sh
+python3 -m unittest discover -s tests -p 'test_host_dns.py' -v
+```
+
+It compiles the actual patched vchroot implementation in its Linux test mode
+and reads temporary resolver files through absolute and relative host symlinks.
+It checks atomic file replacement, symlink retargeting, guest DNS overrides and
+guest absolute-link scope. A CMake fixture verifies that both install modes
+replace an older Google resolver file with the host link. No Darling session or
+DNS traffic is started.
+
 ## CoreText font-list and AppKit resize regressions
 
 After preparing the source and configuring the runtime tools:

docs/TROUBLESHOOTING.md

@@ -192,6 +192,31 @@ observation, without waiting for a match:
 python3 tools/close-league-client-in-game.py --once --dry-run
 ```
 
+### Riot reports NO INTERNET FOUND while the host is online
+
+Older base runtimes ship Google DNS servers (`8.8.8.8` and `8.8.4.4`), which
+some mobile and managed networks block. The base resolver now links to the
+host's `/etc/resolv.conf` through `/Volumes/SystemRoot`, including when the host
+file is a symlink into `/run` for systemd-resolved or NetworkManager. File and
+symlink replacements remain visible without copying the resolver on launch.
+
+Exit Riot and League, then run `./scripts/update.sh` to rebuild and install both
+the base link and the host symlink handling correction. Existing prefix DNS
+overrides in `$DPREFIX/private/etc/resolv.conf` (normally
+`~/.darling/private/etc/resolv.conf`) remain in effect; remove a previous manual
+override with Darling stopped if you want to follow the host instead. A custom
+prefix `/etc` directory can also shadow the base `/etc -> private/etc` link.
+
+Check resolution inside the guest with:
+
+```sh
+darling shell curl --noproxy '*' https://clientconfig.rpg.riotgames.com/
+```
+
+An HTTP response establishes that resolution succeeded even if that endpoint
+rejects the request. This change follows the host resolver configuration;
+already-running clients may cache DNS settings until restarted.
+
 ### Downloads repeatedly fail with an IPv6 CONNECT_TO error
 
 The bundled downloader was observed retrying CDN chunks with:

patches/darling.patch

@@ -11230,10 +11230,21 @@ index 072a6e2..c804100 100755
  
  echo "No instances running now"
 diff --git a/CMakeLists.txt b/CMakeLists.txt
-index 8077b7e..0556080 100644
 --- a/CMakeLists.txt
 +++ b/CMakeLists.txt
-@@ -236,7 +236,12 @@ InstallSymlink(/Volumes/SystemRoot/usr/share/zoneinfo ${CMAKE_INSTALL_PREFIX}/li
+@@ -204,8 +204,9 @@
+ InstallSymlink(private/etc ${CMAKE_INSTALL_PREFIX}/libexec/darling/etc)
+ InstallSymlink(private/var ${CMAKE_INSTALL_PREFIX}/libexec/darling/var)
+ 
+-install(FILES etc/resolv.conf
+-	DESTINATION libexec/darling/private/etc)
++# Follow the host resolver, including local DNS proxies and network changes.
++# Prefix-local resolver overrides still take precedence over this base symlink.
++InstallSymlink(/Volumes/SystemRoot/etc/resolv.conf ${CMAKE_INSTALL_PREFIX}/libexec/darling/private/etc/resolv.conf)
+ InstallSymlink(/Volumes/SystemRoot/etc/machine-id ${CMAKE_INSTALL_PREFIX}/libexec/darling/private/etc/machine-id)
+ InstallSymlink(/Volumes/SystemRoot/etc/nsswitch.conf ${CMAKE_INSTALL_PREFIX}/libexec/darling/private/etc/nsswitch.conf)
+ 
+@@ -236,7 +237,12 @@
  install(DIRECTORY DESTINATION libexec/darling/Library/Preferences)
  
  if(NOT DEBIAN_PACKAGING)

patches/xnu.patch

@@ -6180,3 +6180,23 @@ index 0000000..eb90f43
 +    return true;
 +}
 +#endif
+diff --git a/darling/src/libsystem_kernel/emulation/src/linux_premigration/vchroot_userspace.c b/darling/src/libsystem_kernel/emulation/src/linux_premigration/vchroot_userspace.c
+--- a/darling/src/libsystem_kernel/emulation/src/linux_premigration/vchroot_userspace.c
++++ b/darling/src/libsystem_kernel/emulation/src/linux_premigration/vchroot_userspace.c
+@@ -421,12 +421,14 @@
+ 							ctxt->follow = true;
+ 							ctxt->symlink_depth++;
+ 
+-							// resolve absolute symlinks within the prefix
++							// Keep absolute host symlinks outside the prefix after crossing
++							// /Volumes/SystemRoot (e.g. /etc/resolv.conf -> /run/...).
++							// Resolve guest symlinks within the prefix
+ 							//
+ 							// however, DON'T resolve `/proc` symlinks within the prefix.
+ 							// anything under `/proc` is from Linux's `/proc` since we bind-mount it, so we can special-case them because we want those to be Linux-root relative.
+ 							// see https://github.com/darlinghq/darling/issues/1052 for the issue this works around.
+-							if (link[0] == '/' && !(strncmp(link, "/proc/", 6) == 0 || (rv == 5 && strncmp(link, "/proc", 5) == 0))) {
++							if (link[0] == '/' && ctxt->current_root_len > 0 && !(strncmp(link, "/proc/", 6) == 0 || (rv == 5 && strncmp(link, "/proc", 5) == 0))) {
+ 								ctxt->current_root = prefix_path;
+ 								ctxt->current_root_len = prefix_path_len;
+ 							}

tests/test_host_dns.py

@@ -0,0 +1,133 @@
+"""Exercise the base resolver install and actual vchroot code without DNS traffic."""
+from pathlib import Path
+import os
+import shutil
+import subprocess
+import tempfile
+import unittest
+
+import test_runtime_compatibility as sources
+
+
+@unittest.skipUnless(shutil.which('cc') and shutil.which('patch'), 'C compiler and patch required')
+class HostDNSChecks(unittest.TestCase):
+    patched = sources.CompatibilityChecks.patched
+
+    def setUp(self):
+        self.temporary = tempfile.TemporaryDirectory(prefix='host-dns-')
+        self.addCleanup(self.temporary.cleanup)
+        self.root = Path(self.temporary.name)
+        self.prefix = self.root / 'guest'
+        (self.prefix / 'private/etc').mkdir(parents=True)
+        (self.prefix / 'Volumes/SystemRoot').mkdir(parents=True)
+        (self.prefix / 'etc').symlink_to('private/etc')
+        self.resolver = self.prefix / 'private/etc/resolv.conf'
+
+    def build_vchroot(self):
+        path = 'darling/src/libsystem_kernel/emulation/'
+        source = self.patched('xnu', path + 'src/linux_premigration/vchroot_userspace.c')
+        header = self.root / 'darling/emulation/linux_premigration/vchroot_expand.h'
+        header.parent.mkdir(parents=True)
+        header.write_text(self.patched('xnu', path + 'include/linux_premigration/vchroot_expand.h'))
+        # Use upstream's Linux TEST mode, replacing only its CLI and RPC setup.
+        fixture = r'''
+#define _GNU_SOURCE
+#define TEST
+#include <stdint.h>
+#include <string.h>
+#include <strings.h>
+#include <stdlib.h>
+#define LC_C_LOCALE 0
+#define strncasecmp_l(a,b,n,l) strncasecmp(a,b,n)
+#define __simple_printf printf
+#define __simple_abort abort
+static int dserver_rpc_vchroot_path(char *p, unsigned long n, uint64_t *len) { abort(); }
+#define main upstream_main
+'''
+        fixture += source + r'''
+#undef main
+int main(int argc, const char **argv) {
+    if (argc != 3) return 2;
+    int fd = open(argv[1], O_RDONLY | O_DIRECTORY);
+    if (fd < 0 || __darling_vchroot(fd)) return 3;
+    close(fd);
+    struct vchroot_expand_args args = {.dfd = -100, .flags = VCHROOT_FOLLOW};
+    strcpy(args.path, argv[2]);
+    int result = vchroot_expand(&args);
+    if (result) return 4;
+    FILE *file = fopen(args.path, "r");
+    if (!file) return 5;
+    char buf[4096];
+    while (fgets(buf, sizeof(buf), file)) fputs(buf, stdout);
+    return fclose(file) != 0;
+}
+'''
+        file = self.root / 'check.c'
+        file.write_text(fixture)
+        self.binary = self.root / 'check'
+        result = subprocess.run(['cc', '-std=gnu11', '-I', str(self.root), str(file),
+                                 '-o', str(self.binary)], capture_output=True, text=True)
+        self.assertEqual(result.returncode, 0, result.stderr)
+
+    def read_guest(self, path='/etc/resolv.conf'):
+        result = subprocess.run([str(self.binary), str(self.prefix), path],
+                                capture_output=True, text=True, timeout=10)
+        self.assertEqual(result.returncode, 0, result.stderr)
+        return result.stdout
+
+    def test_host_symlink_chains_updates_and_guest_override(self):
+        self.build_vchroot()
+        host = self.root / 'host'
+        host.mkdir()
+        data = host / 'stub-resolv.conf'
+        data.write_text('nameserver 127.0.0.53\nsearch tether.example\n')
+        self.resolver.symlink_to('/Volumes/SystemRoot' + str(data))
+        self.assertEqual(self.read_guest(), data.read_text())
+        self.resolver.unlink()
+        # An absolute host link followed by a relative one models resolved and
+        # NetworkManager layouts. Never write to the real host resolver.
+        (host / 'relative').symlink_to(data.name)
+        (host / 'resolv.conf').symlink_to(host / 'relative')
+        self.resolver.symlink_to('/Volumes/SystemRoot' + str(host / 'resolv.conf'))
+        self.assertEqual(self.read_guest(), data.read_text())
+        # Network managers replace files atomically; a bind mount or snapshot
+        # would keep reading the old resolver inode.
+        replacement = host / 'next'
+        replacement.write_text('nameserver 192.0.2.53\n')
+        os.replace(replacement, data)
+        self.assertEqual(self.read_guest(), data.read_text())
+        other = host / 'other'
+        other.write_text('nameserver 192.0.2.54\n')
+        (host / 'resolv.conf').unlink()
+        (host / 'resolv.conf').symlink_to(other)
+        self.assertEqual(self.read_guest(), other.read_text())
+        self.resolver.unlink()
+        self.resolver.write_text('nameserver 127.0.0.1\n')
+        self.assertEqual(self.read_guest(), self.resolver.read_text())
+        # Absolute links originating inside the guest must retain guest scope.
+        (self.prefix / 'guest-link').symlink_to('/private/etc/resolv.conf')
+        self.assertEqual(self.read_guest('/guest-link'), self.resolver.read_text())
+
+    @unittest.skipUnless(shutil.which('cmake'), 'CMake required')
+    def test_base_install_replaces_google_file_with_host_link(self):
+        cmake = self.patched('darling', 'CMakeLists.txt')
+        start = cmake.index('# Follow the host resolver')
+        end = cmake.index('\n', cmake.index('InstallSymlink(', start))
+        macro = self.patched('darling', 'cmake/InstallSymlink.cmake')
+        project = self.root / 'project'
+        project.mkdir()
+        (project / 'CMakeLists.txt').write_text(
+            'cmake_minimum_required(VERSION 3.16)\nproject(dns NONE)\n' + macro + '\n' + cmake[start:end] + '\n')
+        base = self.root / 'base'
+        target = base / 'libexec/darling/private/etc/resolv.conf'
+        target.parent.mkdir(parents=True)
+        for packaging in ('OFF', 'ON'):
+            target.unlink(missing_ok=True)
+            target.write_text('nameserver 8.8.8.8\nnameserver 8.8.4.4\n')
+            build = self.root / ('build-' + packaging)
+            subprocess.run(['cmake', '-S', str(project), '-B', str(build),
+                            '-DCMAKE_INSTALL_PREFIX=' + str(base),
+                            '-DBINARY_PACKAGING_MODE=' + packaging], check=True, capture_output=True)
+            subprocess.run(['cmake', '--install', str(build)], check=True, capture_output=True)
+            self.assertTrue(target.is_symlink())
+            self.assertEqual(os.readlink(target), '/Volumes/SystemRoot/etc/resolv.conf')

tests/test_runtime_compatibility.py

@@ -38,7 +38,7 @@ class CompatibilityChecks(unittest.TestCase):
         patch = patch_text.split(marker, 1)[1].split('\ndiff --git ', 1)[0]
         with tempfile.TemporaryDirectory() as folder:
             target = Path(folder) / path
-            target.parent.mkdir(parents=True)
+            target.parent.mkdir(parents=True, exist_ok=True)
             if original is not None:
                 target.write_bytes(original)
             subprocess.run(['patch', '--silent', '-p1', '-d', folder], input=marker + patch + ("" if patch.endswith("\n") else "\n"),

upstream/manifest.json

@@ -274,7 +274,7 @@
       "revision": "fa29287aa2f0115271e091f1031f53c9e024005d",
       "repository": "https://github.com/darlinghq/darling-xnu.git",
       "patch": "patches/xnu.patch",
-      "modified_files": 64,
+      "modified_files": 65,
       "new_files": [
         "darling/src/libsystem_kernel/emulation/include/common/cpu_topology.h",
         "darling/src/libsystem_kernel/emulation/include/common/private_mutex.h",