Add SetCapabilities for setting capabilities to an exact set.

sandbox/linux/services/credentials.h

Index: sandbox/linux/services/credentials.h
diff --git a/sandbox/linux/services/credentials.h b/sandbox/linux/services/credentials.h
index 91435611851f81a0d2136feb3975180d5158874a..2d2ec5de33ee7bef2ce84c6340d788bb35af9198 100644
--- a/sandbox/linux/services/credentials.h
+++ b/sandbox/linux/services/credentials.h
@@ -5,6 +5,8 @@
 #ifndef SANDBOX_LINUX_SERVICES_CREDENTIALS_H_
 #define SANDBOX_LINUX_SERVICES_CREDENTIALS_H_
 
+#include <sys/capability.h>
+
 #include "build/build_config.h"
 // Link errors are tedious to track, raise a compile-time error instead.
 #if defined(OS_ANDROID)
@@ -12,6 +14,7 @@
 #endif  // defined(OS_ANDROID).
 
 #include <string>
+#include <vector>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
@@ -26,7 +29,7 @@ namespace sandbox {
 class SANDBOX_EXPORT Credentials {
  public:
   // Drop all capabilities in the effective, inheritable and permitted sets for
-  // the current process. For security reasons, since capabilities are
+  // the current thread. For security reasons, since capabilities are
   // per-thread, the caller is responsible for ensuring it is single-threaded
   // when calling this API.
   // |proc_fd| must be a file descriptor to /proc/ and remains owned by
@@ -34,11 +37,19 @@ class SANDBOX_EXPORT Credentials {
   static bool DropAllCapabilities(int proc_fd) WARN_UNUSED_RESULT;
   // A similar API which assumes that it can open /proc/self/ by itself.
   static bool DropAllCapabilities() WARN_UNUSED_RESULT;
+  // Sets the effective and permitted capability sets for the current thread to
+  // the list of capabiltiies in |caps|. All other capability flags are cleared.
+  static bool SetCapabilities(int proc_fd, const std::vector<cap_value_t>& caps)
+      WARN_UNUSED_RESULT;
+
+  // Returns true if the current thread has either the CAP_EFFECTIVE or
+  // CAP_PERMITTED flag set for the given capability.
+  static bool HasCapability(cap_value_t cap);
 
   // Return true iff there is any capability in any of the capabilities sets
-  // of the current process.
+  // of the current thread.
   static bool HasAnyCapability();
-  // Returns the capabilities of the current process in textual form, as
+  // Returns the capabilities of the current thread in textual form, as
   // documented in libcap2's cap_to_text(3). This is mostly useful for
   // debugging and tests.
   static scoped_ptr<std::string> GetCurrentCapString();