[Reflection] Sanity-check metadata sizes in MetadataReader before reading. #37863
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…ding. MetadataReader can be given corrupt or garbage data and we need to be able to handle it gracefully. When reading metadata, the full size to read is calculated from partial data. When we're given bad data, these calculated sizes can be enormous, up to 4GB. Trying to read that much data can cause address space exhaustion which leads to unpleasantness. To avoid this, fix a limit of 1MB on metadata sizes, and fail early if the size is larger. No real-world metadata should ever be that large. We also switch these potentially large calls to use the readBytes variant that returns a unique_ptr, rather than allocating a buffer and reading into it. Our clients typically implement that as the primitive, so this avoids an unnecessary extra data copy and extra address space usage for them. Clients that implement reading into a provided buffer as the primitive should see the same performance as before. rdar://78621784
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MetadataReader can be given corrupt or garbage data and we need to be able to handle it gracefully. When reading metadata, the full size to read is calculated from partial data. When we're given bad data, these calculated sizes can be enormous, up to 4GB. Trying to read that much data can cause address space exhaustion which leads to unpleasantness.
To avoid this, fix a limit of 1MB on metadata sizes, and fail early if the size is larger. No real-world metadata should ever be that large.
We also switch these potentially large calls to use the readBytes variant that returns a unique_ptr, rather than allocating a buffer and reading into it. Our clients typically implement that as the primitive, so this avoids an unnecessary extra data copy and extra address space usage for them. Clients that implement reading into a provided buffer as the primitive should see the same performance as before.
rdar://78621784