Make shared memory segment writable only by its rightful owner.

remoting/host/x_server_pixel_buffer.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 "remoting/host/x_server_pixel_buffer.h"
 
 #include <sys/shm.h>
 
 #include "base/logging.h"
 
@@ skipping 103 matching lines @@
   bool using_shm = false;
   shm_segment_info_ = new XShmSegmentInfo;
   shm_segment_info_->shmid = -1;
   shm_segment_info_->shmaddr = reinterpret_cast<char*>(-1);
   shm_segment_info_->readOnly = False;
   x_image_ = XShmCreateImage(display_, default_visual, default_depth, ZPixmap,
                              0, shm_segment_info_, width, height);
   if (x_image_) {
     shm_segment_info_->shmid = shmget(
         IPC_PRIVATE, x_image_->bytes_per_line * x_image_->height,
-        IPC_CREAT | 0666);
+        IPC_CREAT | 0600);
     if (shm_segment_info_->shmid != -1) {
       shm_segment_info_->shmaddr = x_image_->data =
           reinterpret_cast<char*>(shmat(shm_segment_info_->shmid, 0, 0));
       if (x_image_->data != reinterpret_cast<char*>(-1)) {
         EnableXServerErrorTrap();
         using_shm = XShmAttach(display_, shm_segment_info_);
         XSync(display_, False);
         if (GetLastXServerError() != 0)
           using_shm = false;
+        if (using_shm) {
+          VLOG(1) << "Using X shared memory segment "
+                  << shm_segment_info_->shmid;
+        }
       }
+    } else {
+      LOG(WARNING) << "Failed to get shared memory segment. "
+                      "Performance may be degraded.";
     }
   }
 
   if (!using_shm) {
-    VLOG(1) << "Not using shared memory.";
+    LOG(WARNING) << "Not using shared memory. Performance may be degraded.";
     Release();
     return;
   }
 
   if (havePixmaps)
     havePixmaps = InitPixmaps(width, height, default_depth);
 
   shmctl(shm_segment_info_->shmid, IPC_RMID, 0);
   shm_segment_info_->shmid = -1;
 
@@ skipping 99 matching lines @@
 
 int XServerPixelBuffer::GetGreenShift() const {
   return ffs(x_image_->green_mask) - 1;
 }
 
 bool XServerPixelBuffer::IsRgb() const {
   return GetRedShift() == 16 && GetGreenShift() == 8 && GetBlueShift() == 0;
 }
 
 }  // namespace remoting