Linux sandbox: better APIs with /proc/ arguments

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 ed21fd192bd0c7eda1ffaadcbf6583c26f18751d..c8c679d8515e16db91e2636315f3974747b5066a 100644
--- a/sandbox/linux/services/credentials.cc
+++ b/sandbox/linux/services/credentials.cc
@@ -23,7 +23,9 @@
 #include "base/template_util.h"
 #include "base/third_party/valgrind/valgrind.h"
 #include "sandbox/linux/services/namespace_utils.h"
+#include "sandbox/linux/services/proc_util.h"
 #include "sandbox/linux/services/syscall_wrappers.h"
+#include "sandbox/linux/services/thread_helpers.h"
 
 namespace sandbox {
 
@@ -129,7 +131,10 @@ void CheckCloneNewUserErrno(int error) {
 
 }  // namespace.
 
-bool Credentials::DropAllCapabilities() {
+bool Credentials::DropAllCapabilities(int proc_fd) {
+  DCHECK_LE(0, proc_fd);
+  CHECK(ThreadHelpers::IsSingleThreaded(proc_fd));
+
   ScopedCap cap(cap_init());
   CHECK(cap);
   PCHECK(0 == cap_set_proc(cap.get()));
@@ -138,6 +143,11 @@ bool Credentials::DropAllCapabilities() {
   return true;
 }
 
+bool Credentials::DropAllCapabilities() {
+  base::ScopedFD proc_fd(ProcUtil::OpenProc());
+  return Credentials::DropAllCapabilities(proc_fd.get());
+}
+
 bool Credentials::HasAnyCapability() {
   ScopedCap current_cap(cap_get_proc());
   CHECK(current_cap);
@@ -220,9 +230,12 @@ bool Credentials::MoveToNewUserNS() {
   return true;
 }
 
-bool Credentials::DropFileSystemAccess() {
+bool Credentials::DropFileSystemAccess(int proc_fd) {
+  CHECK_LE(0, proc_fd);
+
   CHECK(ChrootToSafeEmptyDir());
   CHECK(!base::DirectoryExists(base::FilePath("/proc")));
+  CHECK(!ProcUtil::HasOpenDirectory(proc_fd));
   // We never let this function fail.
   return true;
 }