From 7cb72c96b4d5ede1b5526a526ccb7dae0490bb0e Mon Sep 17 00:00:00 2001
From: Bernie Innocenti <codewiz@google.com>
Date: Thu, 28 Mar 2019 15:32:37 +0900
Subject: [PATCH] Disallow operator!() on unique_fd

This catches a common mistake where client code checks for errors using
the common idiom that works for std::iostream and other file-like
classes:

  unique_fd fd = open(...);
  if (!fd) {
  }

Test: atest libbase_test
Test: m droid
Change-Id: I9629a7795537ecb3b57be9c741c06f80967e4cc2
---
 base/include/android-base/unique_fd.h | 3 +++
 init/service.cpp                      | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/base/include/android-base/unique_fd.h b/base/include/android-base/unique_fd.h
index 83213e9c4..3fa3bea2e 100644
--- a/base/include/android-base/unique_fd.h
+++ b/base/include/android-base/unique_fd.h
@@ -105,6 +105,9 @@ class unique_fd_impl final {
   int get() const { return fd_; }
   operator int() const { return get(); }  // NOLINT
 
+  // Catch bogus error checks (i.e.: "!fd" instead of "fd != -1").
+  bool operator!() const = delete;
+
   int release() __attribute__((warn_unused_result)) {
     tag(fd_, this, nullptr);
     int ret = fd_;
diff --git a/init/service.cpp b/init/service.cpp
index 6d08cb14a..f5c13b983 100644
--- a/init/service.cpp
+++ b/init/service.cpp
@@ -177,7 +177,7 @@ Result<Success> Service::SetUpPidNamespace() const {
 Result<Success> Service::EnterNamespaces() const {
     for (const auto& [nstype, path] : namespaces_to_enter_) {
         auto fd = unique_fd{open(path.c_str(), O_RDONLY | O_CLOEXEC)};
-        if (!fd) {
+        if (fd == -1) {
             return ErrnoError() << "Could not open namespace at " << path;
         }
         if (setns(fd, nstype) == -1) {