Move a couple of utility functions to a new namespace_utils class.

sandbox/linux/services/credentials.cc

Index: sandbox/linux/services/credentials.cc
diff --git a/sandbox/linux/services/credentials.cc b/sandbox/linux/services/credentials.cc
index 291c2cad4450e9a473281255cde6b72009c3852f..8dda0eb9027a0e506dd80da9e64bbea3b111ff1a 100644
--- a/sandbox/linux/services/credentials.cc
+++ b/sandbox/linux/services/credentials.cc
@@ -22,12 +22,11 @@
 #include "base/process/launch.h"
 #include "base/template_util.h"
 #include "base/third_party/valgrind/valgrind.h"
+#include "sandbox/linux/services/namespace_utils.h"
 #include "sandbox/linux/services/syscall_wrappers.h"
 
 namespace {
 
-bool IsRunningOnValgrind() { return RUNNING_ON_VALGRIND; }
-
 struct CapFreeDeleter {
   inline void operator()(cap_t cap) const {
     int ret = cap_free(cap);
@@ -59,28 +58,6 @@ struct FILECloser {
 // TODO(jln): fix base/.
 typedef scoped_ptr<FILE, FILECloser> ScopedFILE;
 
-static_assert((base::is_same<uid_t, gid_t>::value),
-              "uid_t and gid_t should be the same type");
-// generic_id_t can be used for either uid_t or gid_t.
-typedef uid_t generic_id_t;
-
-// Write a uid or gid mapping from |id| to |id| in |map_file|.
-bool WriteToIdMapFile(const char* map_file, generic_id_t id) {
-  ScopedFILE f(fopen(map_file, "w"));
-  PCHECK(f);
-  const uid_t inside_id = id;
-  const uid_t outside_id = id;
-  int num = fprintf(f.get(), "%d %d 1\n", inside_id, outside_id);
-  if (num < 0) return false;
-  // Manually call fflush() to catch permission failures.
-  int ret = fflush(f.get());
-  if (ret) {
-    VLOG(1) << "Could not write to id map file";
-    return false;
-  }
-  return true;
-}
-
 // Checks that the set of RES-uids and the set of RES-gids have
 // one element each and return that element in |resuid| and |resgid|
 // respectively. It's ok to pass NULL as one or both of the ids.
@@ -168,37 +145,6 @@ scoped_ptr<std::string> Credentials::GetCurrentCapString() {
   return scoped_ptr<std::string> (new std::string(cap_text.get()));
 }
 
-// static
-bool Credentials::SupportsNewUserNS() {
-  // Valgrind will let clone(2) pass-through, but doesn't support unshare(),
-  // so always consider UserNS unsupported there.
-  if (IsRunningOnValgrind()) {
-    return false;
-  }
-
-  // This is roughly a fork().
-  const pid_t pid = sys_clone(CLONE_NEWUSER | SIGCHLD, 0, 0, 0, 0);
-
-  if (pid == -1) {
-    CheckCloneNewUserErrno(errno);
-    return false;
-  }
-
-  // The parent process could have had threads. In the child, these threads
-  // have disappeared. Make sure to not do anything in the child, as this is a
-  // fragile execution environment.
-  if (pid == 0) {
-    _exit(0);
-  }
-
-  // Always reap the child.
-  siginfo_t infop;
-  PCHECK(0 == HANDLE_EINTR(waitid(P_PID, pid, &infop, WEXITED)));
-
-  // clone(2) succeeded, we can use CLONE_NEWUSER.
-  return true;
-}
-
 bool Credentials::MoveToNewUserNS() {
   uid_t uid;
   gid_t gid;
@@ -222,8 +168,8 @@ bool Credentials::MoveToNewUserNS() {
   DCHECK(GetRESIds(NULL, NULL));
   const char kGidMapFile[] = "/proc/self/gid_map";
   const char kUidMapFile[] = "/proc/self/uid_map";
-  CHECK(WriteToIdMapFile(kGidMapFile, gid));
-  CHECK(WriteToIdMapFile(kUidMapFile, uid));
+  CHECK(NamespaceUtils::WriteToIdMapFile(kGidMapFile, gid));
+  CHECK(NamespaceUtils::WriteToIdMapFile(kUidMapFile, uid));
   DCHECK(GetRESIds(NULL, NULL));
   return true;
 }