Use safer IPC serializations in media_param_traits.cc

media/audio/audio_parameters.cc

Index: media/audio/audio_parameters.cc
diff --git a/media/audio/audio_parameters.cc b/media/audio/audio_parameters.cc
index c9dcdeb7e5f6ce66db2c93c7dbd6ecb490f3db67..872413f808379b92ad460be125340d26b7735c6a 100644
--- a/media/audio/audio_parameters.cc
+++ b/media/audio/audio_parameters.cc
@@ -68,12 +68,8 @@ void AudioParameters::Reset(Format format, ChannelLayout channel_layout,
 }
 
 bool AudioParameters::IsValid() const {
-  return (format_ >= AUDIO_PCM_LINEAR) &&
-         (format_ < AUDIO_LAST_FORMAT) &&

[dcheng, 2015/06/29 21:46:55]

Removing these two lines causes two unit tests to fail.

I have ask: what is the value of those unit tests? You have to do clearly
invalid things to get it to fail (convert an out-of-range int to an enum value
by casting it). The only way this could happen normally is:
1) Someone checks in extremely broken code. AudioParameters::IsValid() is a weak
defense against this anyway.
2) Some serialization/deserialization routine forgets to sanity check this. But
the only place we should be serializing/deserializing this is via IPC messages?
So I don't see how this could happen either.

Given this, would it make sense to just remove the unit tests in question?

[xhwang, 2015/06/29 23:53:15]

I agree :)

[Tom Sepez, 2015/06/30 15:37:07]

Now that the enums are being checked by IPC itself, we avoid the situation that
a crafted message from an untrusted process (renderer) could reach a trusted
browser process.  IsValid() would have to guard against that in the past, but it
doesn't anymore.

[dcheng, 2015/06/30 18:11:59]

I just wanted to make sure that media code wasn't using IsValid() in unexpected
ways before I removed the tests for "invalid foramt".

Done!

-         (channels_ > 0) &&
-         (channels_ <= media::limits::kMaxChannels) &&
+  return (channels_ > 0) && (channels_ <= media::limits::kMaxChannels) &&
          (channel_layout_ > CHANNEL_LAYOUT_UNSUPPORTED) &&
-         (channel_layout_ <= CHANNEL_LAYOUT_MAX) &&
          (sample_rate_ >= media::limits::kMinSampleRate) &&
          (sample_rate_ <= media::limits::kMaxSampleRate) &&
          (bits_per_sample_ > 0) &&