AppArmor profile per binary path with install hint; verified network examples

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/sandbox.cpp

@@ -15,6 +15,7 @@
 #include <unistd.h>
 
 #include <cstring>
+#include <fstream>
 
 #include <poll.h>
 #include <algorithm>
@@ -293,12 +294,60 @@ int containerInit(void* arg) {
         ::_exit(code);
     } catch (const std::exception& e) {
         ::dprintf(2, "doos: %s\n", e.what());
+        auto* se = dynamic_cast<const SysError*>(&e);
+        std::ifstream restrictUserns("/proc/sys/kernel/apparmor_restrict_unprivileged_userns");
+        int restricted = 0;
+        if (restrictUserns) restrictUserns >> restricted;
+        if (se && (se->code() == EPERM || se->code() == EACCES) && restricted == 1) {
+            ::dprintf(2, "doos: AppArmor restricts user namespaces for this binary. Install a profile once with:\n  %s\n",
+                      Sandbox::apparmorInstallHint().c_str());
+        }
         ::_exit(125);
     }
 }
 
 }  // namespace
 
+namespace {
+fs::path selfPath() {
+    std::error_code ec;
+    fs::path self = fs::read_symlink("/proc/self/exe", ec);
+    if (ec) throw std::runtime_error("cannot resolve the path of this binary: " + ec.message());
+    std::string path = self.string();
+    if (path.find_first_of("{}[]*?\"\n,") != std::string::npos) {
+        throw std::runtime_error("binary path contains characters AppArmor treats as globs: " + path);
+    }
+    return self;
+}
+
+// One profile per binary path, so installing doos in a second place does not replace the first profile.
+std::string profileName(const fs::path& self) {
+    std::string n = "doos" + self.string();
+    for (auto& c : n) {
+        if (c == '/') c = '-';
+    }
+    return n;
+}
+}  // namespace
+
+std::string Sandbox::apparmorProfile() {
+    fs::path self = selfPath();
+    return "# Lets doos use unprivileged user namespaces where kernel.apparmor_restrict_unprivileged_userns=1.\n"
+           "# Generated by: doos apparmor   (profile is for exactly this path)\n"
+           "abi <abi/5.0>,\n"
+           "include <tunables/global>\n"
+           "\n"
+           "profile " + profileName(self) + " " + self.string() + " flags=(unconfined) {\n"
+           "  userns,\n"
+           "  @{exec_path} mr,\n"
+           "}\n";
+}
+
+std::string Sandbox::apparmorInstallHint() {
+    std::string file = "/etc/apparmor.d/" + profileName(selfPath());
+    return "doos apparmor | sudo tee " + file + " >/dev/null && sudo apparmor_parser -r " + file;
+}
+
 int Sandbox::run() {
     if (command_.size() > spec::kMaxCommandArgs) throw std::runtime_error("too many command arguments");
     // Decide start-or-join under the lock so concurrent attaches agree.