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

sandbox/linux/services/credentials.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sandbox/linux/services/credentials.h"
 
 #include <errno.h>
 #include <signal.h>
 #include <stdio.h>
 #include <sys/capability.h>
 #include <sys/syscall.h>
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/template_util.h"
 #include "base/third_party/valgrind/valgrind.h"
 #include "base/threading/thread.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);
     CHECK_EQ(0, ret);
   }
 };
 
 // Wrapper to manage libcap2's cap_t type.
 typedef scoped_ptr<typeof(*((cap_t)0)), CapFreeDeleter> ScopedCap;
 
@@ skipping 11 matching lines @@
   inline void operator()(FILE* f) const {
     DCHECK(f);
     PCHECK(0 == fclose(f));
   }
 };
 
 // Don't use ScopedFILE in base since it doesn't check fclose().
 // 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.
 bool GetRESIds(uid_t* resuid, gid_t* resgid) {
   uid_t ruid, euid, suid;
   gid_t rgid, egid, sgid;
   PCHECK(getresuid(&ruid, &euid, &suid) == 0);
   PCHECK(getresgid(&rgid, &egid, &sgid) == 0);
   const bool uids_are_equal = (ruid == euid) && (ruid == suid);
   const bool gids_are_equal = (rgid == egid) && (rgid == sgid);
@@ skipping 82 matching lines @@
 }
 
 scoped_ptr<std::string> Credentials::GetCurrentCapString() {
   ScopedCap current_cap(cap_get_proc());
   CHECK(current_cap);
   ScopedCapText cap_text(cap_to_text(current_cap.get(), NULL));
   CHECK(cap_text);
   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;
   if (!GetRESIds(&uid, &gid)) {
     // If all the uids (or gids) are not equal to each other, the security
     // model will most likely confuse the caller, abort.
     DVLOG(1) << "uids or gids differ!";
     return false;
   }
   int ret = unshare(CLONE_NEWUSER);
   if (ret) {
     const int unshare_errno = errno;
     VLOG(1) << "Looks like unprivileged CLONE_NEWUSER may not be available "
             << "on this kernel.";
     CheckCloneNewUserErrno(unshare_errno);
     return false;
   }
 
   // The current {r,e,s}{u,g}id is now an overflow id (c.f.
   // /proc/sys/kernel/overflowuid). Setup the uid and gid maps.
   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;
 }
 
 bool Credentials::DropFileSystemAccess() {
   return ChrootToSafeEmptyDir();
 }
 
 }  // namespace sandbox.