Add TaskForPID()

util/mach/task_for_pid.h

Index: util/mach/task_for_pid.h
diff --git a/util/mach/task_for_pid.h b/util/mach/task_for_pid.h
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+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef CRASHPAD_UTIL_MACH_TASK_FOR_PID_H_
+#define CRASHPAD_UTIL_MACH_TASK_FOR_PID_H_
+
+#include <mach/mach.h>
+#include <sys/types.h>
+
+namespace crashpad {
+
+//! \brief Wraps `task_for_pid()`.
+//!
+//! This function exists to support `task_for_pid()` access checks in a setuid
+//! environment. Normally, `task_for_pid()` can only return an arbitrary task’s
+//! port when running as root or when taskgated(8) approves. When not running as
+//! root, a series of access checks are perfomed to ensure that the running
+//! process has permission to obtain the other process’ task port.
+//!
+//! It is possible to make an executable setuid root to give it broader
+//! `task_for_pid()` access by bypassing taskgated(8) checks, but this also has
+//! the effect of bypassing the access checks, allowing any process’ task port
+//! to be obtained. In most situations, these access checks are desirable to
+//! prevent security and privacy breaches.
+//!
+//! When running as setuid root, this function wraps `task_for_pid()`,
+//! reimplementing those access checks. A process whose effective user ID is 0
+//! and whose real user ID is nonzero is understood to be running setuid root.
+//! In this case, the requested task’s real, effective, and saved set-user IDs
+//! must all equal the running process’ real user ID, the requested task must
+//! not have changed privileges, and the requested task’s set of all group IDs
+//! (including its real, effective, and saved set-group IDs and supplementary
+//! group list) must be a subset of the running process’ set of all group IDs.
+//! These access checks mimic those that the kernel performs.
+//!
+//! When not running as setuid root, `task_for_pid()` is called directly,
+//! without imposing any additional checks beyond what the kernel does.
+//!
+//! \param[in] pid The process ID of the task whose task port is desired.
+//!
+//! \return A send right to the task port if it could be obtained, or
+//!     `TASK_NULL` otherwise, with an error message logged. If a send right is
+//!     returned, the caller takes ownership of it.
+task_t TaskForPID(pid_t pid);
+
+}  // namespace crashpad
+
+#endif  // CRASHPAD_UTIL_MACH_TASK_FOR_PID_H_