Correctly align memory allocations in the case where we need to allocate memo...

sandbox/linux/seccomp/maps.cc

 // Copyright (c) 2010 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 <errno.h>
 #include <fcntl.h>
 #include <iostream>
 #include <linux/unistd.h>
 #include <signal.h>
 #include <stdarg.h>
@@ skipping 203 matching lines @@
             unsigned long position;
             if (isStackLine(ptr, buf + len)) {
               // If we're adjacent to the stack, try to stay away from
               // the GROWS_DOWN region.  Pick the farthest away region that
               // is still within the gap.
 
               if (static_cast<unsigned long>(addr) < kMaxDistance ||  // Underflow protection.
                   static_cast<unsigned long>(addr) - kMaxDistance < gap_start) {
                 position = gap_start;
               } else {
-                position = addr - kMaxDistance;
+                position = (addr - kMaxDistance) & ~4095;
+                if (position < gap_start) {
+                  position = gap_start;
+                }
               }
             } else {
               // Otherwise, take the end of the region.
               position = gap_end - size;
             }
             new_addr = reinterpret_cast<char *>(sys.MMAP
                            (reinterpret_cast<void *>(position), size, prot,
                             MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, -1, 0));
             if (new_addr != MAP_FAILED) {
               goto done;
@@ skipping 21 matching lines @@
         break;
       }
     }
   } while (len || long_line);
   new_addr = NULL;
 done:
   return reinterpret_cast<char*>(new_addr);
 }
 
 } // namespace