Backport http://codereview.chromium.org/8800025 to fix issues with noexec /dev/shm
diff --git a/base/file_util.h b/base/file_util.h
index 90ec1ae..78827e9 100644
--- a/base/file_util.h
+++ b/base/file_util.h
@@ -259,7 +259,7 @@ BASE_EXPORT bool IsDirectoryEmpty(const FilePath& dir_path);
 BASE_EXPORT bool GetTempDir(FilePath* path);
 // Get a temporary directory for shared memory files.
 // Only useful on POSIX; redirects to GetTempDir() on Windows.
-BASE_EXPORT bool GetShmemTempDir(FilePath* path);
+BASE_EXPORT bool GetShmemTempDir(FilePath* path, bool executable);
 
 // Get the home directory.  This is more complicated than just getenv("HOME")
 // as it knows to fall back on getpwent() etc.
@@ -279,7 +279,10 @@ BASE_EXPORT bool CreateTemporaryFileInDir(const FilePath& dir,
 // Returns a handle to the opened file or NULL if an error occured.
 BASE_EXPORT FILE* CreateAndOpenTemporaryFile(FilePath* path);
 // Like above but for shmem files.  Only useful for POSIX.
-BASE_EXPORT FILE* CreateAndOpenTemporaryShmemFile(FilePath* path);
+// The executable flag says the file needs to support using
+// mprotect with PROT_EXEC after mapping.
+BASE_EXPORT FILE* CreateAndOpenTemporaryShmemFile(FilePath* path,
+                                                  bool executable);
 // Similar to CreateAndOpenTemporaryFile, but the file is created in |dir|.
 BASE_EXPORT FILE* CreateAndOpenTemporaryFileInDir(const FilePath& dir,
                                                   FilePath* path);
diff --git a/base/file_util_android.cc b/base/file_util_android.cc
index eff3a46..6807d8d 100644
--- a/base/file_util_android.cc
+++ b/base/file_util_android.cc
@@ -8,7 +8,7 @@
 
 namespace file_util {
 
-bool GetShmemTempDir(FilePath* path) {
+bool GetShmemTempDir(FilePath* path, bool executable) {
   *path = FilePath("/data/local/tmp");
   return true;
 }
diff --git a/base/file_util_mac.mm b/base/file_util_mac.mm
index 95d4f25..bb4975d 100644
--- a/base/file_util_mac.mm
+++ b/base/file_util_mac.mm
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
@@ -22,7 +22,7 @@ bool GetTempDir(FilePath* path) {
   return true;
 }
 
-bool GetShmemTempDir(FilePath* path) {
+bool GetShmemTempDir(FilePath* path, bool executable) {
   return GetTempDir(path);
 }
 
diff --git a/base/file_util_posix.cc b/base/file_util_posix.cc
index 582f70e..5c14abd 100644
--- a/base/file_util_posix.cc
+++ b/base/file_util_posix.cc
@@ -481,9 +481,9 @@ bool CreateTemporaryFile(FilePath* path) {
   return true;
 }
 
-FILE* CreateAndOpenTemporaryShmemFile(FilePath* path) {
+FILE* CreateAndOpenTemporaryShmemFile(FilePath* path, bool executable) {
   FilePath directory;
-  if (!GetShmemTempDir(&directory))
+  if (!GetShmemTempDir(&directory, executable))
     return NULL;
 
   return CreateAndOpenTemporaryFileInDir(directory, path);
@@ -910,15 +910,52 @@ bool GetTempDir(FilePath* path) {
 }
 
 #if !defined(OS_ANDROID)
-bool GetShmemTempDir(FilePath* path) {
+
 #if defined(OS_LINUX)
-  *path = FilePath("/dev/shm");
-  return true;
-#else
-  return GetTempDir(path);
-#endif
+// Determine if /dev/shm files can be mapped and then mprotect'd PROT_EXEC.
+// This depends on the mount options used for /dev/shm, which vary among
+// different Linux distributions and possibly local configuration.  It also
+// depends on details of kernel--ChromeOS uses the noexec option for /dev/shm
+// but its kernel allows mprotect with PROT_EXEC anyway.
+
+namespace {
+
+bool DetermineDevShmExecutable() {
+  bool result = false;
+  FilePath path;
+  int fd = CreateAndOpenFdForTemporaryFile(FilePath("/dev/shm"), &path);
+  if (fd >= 0) {
+    ScopedFD shm_fd_closer(&fd);
+    Delete(path, false);
+    size_t pagesize = sysconf(_SC_PAGESIZE);
+    void *mapping = mmap(NULL, pagesize, PROT_READ, MAP_SHARED, fd, 0);
+    if (mapping != MAP_FAILED) {
+      if (mprotect(mapping, pagesize, PROT_READ | PROT_EXEC) == 0)
+        result = true;
+      munmap(mapping, pagesize);
+    }
+  }
+  return result;
 }
+
+};  // namespace
+#endif  // defined(OS_LINUX)
+
+bool GetShmemTempDir(FilePath* path, bool executable) {
+#if defined(OS_LINUX)
+  bool use_dev_shm = true;
+  if (executable) {
+    static const bool s_dev_shm_executable = DetermineDevShmExecutable();
+    use_dev_shm = s_dev_shm_executable;
+  }
+  if (use_dev_shm) {
+    *path = FilePath("/dev/shm");
+    return true;
+  }
 #endif
+  return GetTempDir(path);
+}
+#endif  // !defined(OS_ANDROID)
 
 FilePath GetHomeDir() {
   const char* home_dir = getenv("HOME");
diff --git a/base/file_util_unittest.cc b/base/file_util_unittest.cc
index 00cacd6..a9f9377 100644
--- a/base/file_util_unittest.cc
+++ b/base/file_util_unittest.cc
@@ -1545,7 +1545,7 @@ TEST_F(FileUtilTest, CreateNewTemporaryDirInDirTest) {
 
 TEST_F(FileUtilTest, GetShmemTempDirTest) {
   FilePath dir;
-  EXPECT_TRUE(file_util::GetShmemTempDir(&dir));
+  EXPECT_TRUE(file_util::GetShmemTempDir(&dir, false));
   EXPECT_TRUE(file_util::DirectoryExists(dir));
 }
 
diff --git a/base/file_util_win.cc b/base/file_util_win.cc
index 8d9fbde..a6720a5 100644
--- a/base/file_util_win.cc
+++ b/base/file_util_win.cc
@@ -556,7 +556,7 @@ bool GetTempDir(FilePath* path) {
   return true;
 }
 
-bool GetShmemTempDir(FilePath* path) {
+bool GetShmemTempDir(FilePath* path, bool executable) {
   return GetTempDir(path);
 }
 
@@ -576,7 +576,7 @@ bool CreateTemporaryFile(FilePath* path) {
   return false;
 }
 
-FILE* CreateAndOpenTemporaryShmemFile(FilePath* path) {
+FILE* CreateAndOpenTemporaryShmemFile(FilePath* path, bool executable) {
   base::ThreadRestrictions::AssertIOAllowed();
   return CreateAndOpenTemporaryFile(path);
 }
diff --git a/base/shared_memory_posix.cc b/base/shared_memory_posix.cc
index 030061a..a66c859 100644
--- a/base/shared_memory_posix.cc
+++ b/base/shared_memory_posix.cc
@@ -123,7 +123,7 @@ bool SharedMemory::Create(const SharedMemoryCreateOptions& options) {
     DCHECK(!options.open_existing);
     // Q: Why not use the shm_open() etc. APIs?
     // A: Because they're limited to 4mb on OS X.  FFFFFFFUUUUUUUUUUU
-    fp = file_util::CreateAndOpenTemporaryShmemFile(&path);
+    fp = file_util::CreateAndOpenTemporaryShmemFile(&path, options.executable);
 
     // Deleting the file prevents anyone else from mapping it in
     // (making it private), and prevents the need for cleanup (once
@@ -317,7 +317,7 @@ bool SharedMemory::FilePathForMemoryName(const std::string& mem_name,
   DCHECK_EQ(std::string::npos, mem_name.find('\0'));
 
   FilePath temp_dir;
-  if (!file_util::GetShmemTempDir(&temp_dir))
+  if (!file_util::GetShmemTempDir(&temp_dir, false))
     return false;
 
 #if !defined(OS_MACOSX)
-- 
1.7.6.1