fix: Verify MemoryShm::byte_size inside shared memory boundary

[yinggeh]

What does the PR do?

When attacker registers the same shm created by python backend, they can overwrite MemoryShm::byte_size data with a very large value. Identity model will read a large chunk of sensitive data (e.g. glibc.so) as input tensor, copy to the output tensor and send back to the client.

Checklist

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Commit Type:

• fix

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Where should the reviewer start?

Test plan:

• CI Pipeline ID:
  30911637

Caveats:

Background

Related Issues: (use one of the action keywords Closes / Fixes / Resolves / Relates to)

• closes GitHub issue: #xxx

[yinggeh]

No unit test because triton-inference-server/server#8273 makes the exploitation impossible.