Setuid sandbox API versioning

content/zygote/zygote_main_linux.cc

 // Copyright (c) 2012 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 <dlfcn.h>
 #include <fcntl.h>
 #include <pthread.h>
 #include <stdio.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
@@ skipping 486 matching lines @@
 static bool EnterSandbox(bool* using_suid_sandbox, bool* has_started_new_init) {
   *using_suid_sandbox = false;
   *has_started_new_init = false;
 
   PreSandboxInit();
   SkiaFontConfigSetImplementation(
       new FontConfigIPC(Zygote::kMagicSandboxIPCDescriptor));
 
   const char* const sandbox_fd_string = getenv(kSUIDSandboxVar);
   if (sandbox_fd_string) {
+    char* endptr;
     // Use the SUID sandbox.  This still allows the seccomp sandbox to
     // be enabled by the process later.
     *using_suid_sandbox = true;
 
-    char* endptr;
+    // Check if the SUID sandbox provides the correct API version.
+    const char* const sandbox_api_string =
+                        getenv(base::kSandboxEnvironmentApiProvides);
+    // Assume API version 0 if no environment was found
+    long sandbox_api_num = 0;
+    if (sandbox_api_string) {
+      errno = 0;
+      sandbox_api_num = strtol(sandbox_api_string, &endptr, 10);
+      if (errno || *endptr) {
+        return false;
+      }
+    }
+
+    if (sandbox_api_num != base::kSUIDSandboxApiNumber) {
+      LOG(WARNING) << "You are using a wrong version of the setuid binary!\n"
+       "Please read "
+       "https://code.google.com/p/chromium/wiki/LinuxSUIDSandboxDevelopment."
+       "\n\n";
+    }
+
+    // Get the file descriptor to signal the chroot helper.
+    errno = 0;
     const long fd_long = strtol(sandbox_fd_string, &endptr, 10);
-    if (!*sandbox_fd_string || *endptr || fd_long < 0 || fd_long > INT_MAX)
+    if (errno || !*sandbox_fd_string || *endptr || fd_long < 0 ||
+        fd_long > INT_MAX) {
       return false;
+    }
     const int fd = fd_long;
 
     static const char kMsgChrootMe = 'C';
     static const char kMsgChrootSuccessful = 'O';
 
     if (HANDLE_EINTR(write(fd, &kMsgChrootMe, 1)) != 1) {
       LOG(ERROR) << "Failed to write to chroot pipe: " << errno;
       return false;
     }
 
@@ skipping 140 matching lines @@
     }
   }
 #endif  // SECCOMP_SANDBOX
 
   Zygote zygote(sandbox_flags, forkdelegate, proc_fd_for_seccomp);
   // This function call can return multiple times, once per fork().
   return zygote.ProcessRequests();
 }
 
 }  // namespace content