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mohammadmseet-hue
675162556b
`PtrRecord::ReadPtrName()` reads a PTR target's first label with
`Name::ReadLabel()`, which performs no emptiness check. A response whose
first label is a single NUL byte (wire `01 00`) is stored as an empty
C-string and cached by the browse cache as a service instance. When the
cache later builds a known-answer question, it calls
`Name::AppendLabel("")`, which returns `kErrorInvalidArgs`; the
surrounding `SuccessOrAssert()` turns that into an abort. A single
unauthenticated link-local mDNS response thus crashes any node with an
active browser.
Reject an empty first label in `ReadPtrName()` so the record is dropped
on receive and never cached. This matches the `Name::ValidateLabel`
checks already applied on the registration and resolver paths, and makes
the "ReadPtrName() validates that PTR record is well-formed" comment at
the call site accurate.
Add a regression test that delivers a PTR response with a single
NUL-byte instance label and verifies no result is reported and the
browser keeps querying without the malformed entry.