Use after free in `DecodePng` kernel

Impact

A malicious user can cause a use after free behavior when [decoding PNG images](https://github.com/tensorflow/tensorflow/blob/a1320ec1eac186da1d03f033109191f715b2b130/tensorflow/core/kernels/image/decode_image_op.cc#L339-L346):

```cc

if (/* ... error conditions ... */) {

png::CommonFreeDecode(&decode);

OP_REQUIRES(context, false,

errors::InvalidArgument("PNG size too large for int: ",

decode.width, " by ", decode.height));

}

`

After png::CommonFreeDecode(&decode) gets called, the values of decode.width and decode.height are in an unspecified state.

Patches

We have patched the issue in GitHub commit [e746adbfcfee15e9cfdb391ff746c765b99bdf9b](https://github.com/tensorflow/tensorflow/commit/e746adbfcfee15e9cfdb391ff746c765b99bdf9b).

The fix will be included in TensorFlow 2.8.0. We will also cherrypick this commit on TensorFlow 2.7.1, TensorFlow 2.6.3, and TensorFlow 2.5.3, as these are also affected and still in supported range.

For more information

Please consult [our security guide](https://github.com/tensorflow/tensorflow/blob/master/SECURITY.md) for more information regarding the security model and how to contact us with issues and questions.