Prevent reading or writing OpenEXR images with no channels #911
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Address https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=30115
OpenEXR images were always supposed to have at least one channel. This change adds the missing sanity check to prevent reading or writing files with no channel list, or with an empty channel list.
It is theoretically possible to create a file with an empty channel list, but it will always be flagged as incomplete.
Since such files are non-standard and unexpected, software reading such files may misbehave in ways that could be exploited.
For safety, it seems safer to add the explicit check to prevent handling such files.
For future-proofing, this test only runs on known types. In the future a new OpenEXR library may add a new 'part type' that does not contain a channel list attribute. Files with such parts would pass this sanity check so they could be (partially) loaded by existing versions of the library.
Signed-off-by: Peter Hillman peterh@wetafx.co.nz