Returns an error immediately without sending IPC message when a font family name to resolve is too long.

This change is important when a site has @font-face rule like:

  // http://paulirish.com/webkit-fontface-hang.html
  @font-face{font-family:testfont;src:url('data:font/ttf;base64,AA.....<<looooooooooong base64 data>>.....aQ==')}

In such a case, WebCore first calls SkFontHost::CreateTypeface() with the (possibly very long) data-uri string itself, then calls SkFontHost::CreateTypefaceFromStream() with decoded byte stream. Since render_sandbox_host_linux.cc just ignores too long IPC message, the renderer process could block indefinitely waiting for a reply inside recvmsg() system call called from SkFontHost::CreateTypeface().

I'm not sure if the WebCore behavior (i.e. calling CreateTypeface with data-uris) is reasonable, but I believe the Skia part is better to be fixed anyway. Non data-uri font family names could be very long too:

  @font-face{font-family:testfont;src:local('AA........AA');}

BUG=29861
TEST=First, set up your Linux SUID Sandbox binary: http://code.google.com/p/chromium/wiki/LinuxSUIDSandboxDevelopment. Then start Chromium and visit http://paulirish.com/webkit-fontface-hang.html or http://typekit.com/. Verify that the renderer does not freeze.

Review URL: http://codereview.chromium.org/507037

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@34915 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 12 insertions, 3 deletions

diff --git a/chrome/browser/renderer_host/render_sandbox_host_linux.cc b/chrome/browser/renderer_host/render_sandbox_host_linux.cc
index f1c3b03..2e89799 100644
--- a/chrome/browser/renderer_host/render_sandbox_host_linux.cc
+++ b/chrome/browser/renderer_host/render_sandbox_host_linux.cc
@@ -100,11 +100,20 @@ class SandboxIPCProcess  {
 
   void HandleRequestFromRenderer(int fd) {
     std::vector<int> fds;
-    static const unsigned kMaxMessageLength = 2048;
-    char buf[kMaxMessageLength];
+
+    // A FontConfigIPC::METHOD_MATCH message could be kMaxFontFamilyLength
+    // bytes long (this is the largest message type).
+    // 128 bytes padding are necessary so recvmsg() does not return MSG_TRUNC
+    // error for a maximum length message.
+    char buf[FontConfigInterface::kMaxFontFamilyLength + 128];
+
     const ssize_t len = base::RecvMsg(fd, buf, sizeof(buf), &fds);
-    if (len == -1)
+    if (len == -1) {
+      // TODO: should send an error reply, or the sender might block forever.
+      NOTREACHED()
+          << "Sandbox host message is larger than kMaxFontFamilyLength";
       return;
+    }
     if (fds.size() == 0)
       return;