Linux sandbox: add a new low-level broker process mechanism.

sandbox/linux/services/broker_process.h

+#ifndef SANDBOX_LINUX_SERVICES_OPEN_BROKER_H_
+#define SANDBOX_LINUX_SERVICES_OPEN_BROKER_H_
+
+#include <string>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/process.h"
+
+namespace sandbox {
+
+// Create a new "broker" process to which we can send requests via an IPC
+// channel.
+// This is a low level IPC mechanism that is suitable to be called from a
+// signal handler.
+// A process would typically create a broker process before entering
+// sandboxing.
+// 1. BrokerProcess open_broker(file_whitelist);
+// 2. CHECK(open_broker.Init(NULL));
+// 3. Enable sandbox.
+// 4. Use open_broker.Open() to open files.
+class BrokerProcess {
+ public:
+  static const int kMaxMessageLength = 4096;
+  static const int kCommandOpen = 'O';
+
+  // allowed_file_names is a white list of files that can be opened later via
+  // the Open() API.
+  explicit BrokerProcess(const std::vector<std::string>& allowed_file_names);
+  // The constructor below should be reserved for unit tests.
+  BrokerProcess(const std::vector<std::string>& allowed_file_names,
+                bool fast_check_in_client);
+  ~BrokerProcess();
+  // Will initialize the broker process. There should be no threads at this
+  // point, since we need to fork().
+  // sandbox_callback should be NULL as this feature is not implemented yet.
+  bool Init(void* sandbox_callback);
+
+  // Can be used in lieu of open(). Will be async signal safe.
+  // The implementation only supports O_RDONLY for now.

[Jorge Lucangeli Obes, 2012/12/13 02:14:54]

I need to check if the /dev/dri/card0 thing libva was opening was being opened
RDONLY.

[jln (very slow on Chromium), 2012/12/13 02:33:14]

Ok. It's trivial to add support for RD_WRITE anyway. Let me know if I should do
it right now.

[Jorge Lucangeli Obes (Google), 2012/12/13 04:28:52]

Confirmed libva is opening /dev/dri/card0 O_RDWR.

+  // It's similar to the open() system call and will return -errno.
+  int Open(const char* pathname, int flags) const;
+
+  int broker_pid() const { return broker_pid_; }
+
+ private:
+  BrokerProcess();
+  bool initialized_;  // Whether we've been through Init() yet.
+  bool is_child_;  // Whether we're the child (broker process).
+  bool fast_check_in_client_;  // Whether to forward a request that we know
+                               // will be denied to the broker.
+  pid_t broker_pid_;  // The PID of the broker (child).
+  std::vector<std::string> allowed_file_names_;
+  int ipc_socketpair_;  // Our communication channel to parent or child.
+  DISALLOW_COPY_AND_ASSIGN(BrokerProcess);
+};
+
+}  // namespace sandbox
+
+#endif  // SANDBOX_LINUX_SERVICES_OPEN_BROKER_H_