Bound the checkpoint size accepted by the migration endpoint#264
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handle_migration_connection read the peer-declared blob_len into memory before the HMAC could be verified, with no upper bound, so an unauthenticated peer could make the endpoint buffer arbitrarily large payloads. Reject declarations above a configurable max_blob_len (default 64 MiB) before reading the body. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01DDSofWX5HwawsrwbN2nSXR
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Issue
handle_migration_connectionvalidates that the peer-declaredblob_lenis a non-negative integer, but puts no upper bound on it. The endpoint then calls_read_exact(conn, blob_len), which buffers the entire body in memory — and the HMAC authenticator can only be verified after that read completes. An unauthenticated peer can therefore declare an arbitrarily large checkpoint and make the migration endpoint buffer unbounded data, the same class of resource-exhaustion issueSecureChannelalready guards against with its length-prefix bound.Fix
max_blob_lenparameter (defaultDEFAULT_MAX_BLOB_LEN= 64 MiB) tohandle_migration_connectionandserve_migration_once.MigrationProtocolError("checkpoint exceeds maximum size")before reading the body; the endpoint's existing error handling converts this into anok=Falseresponse.Testing
test_endpoint_rejects_oversized_checkpoint_before_reading_itverifies the rejection response is sent without the body being read and thatrestore_fnnever runs.🤖 Generated with Claude Code
https://claude.ai/code/session_01DDSofWX5HwawsrwbN2nSXR
Generated by Claude Code