wire: bound decoded auth.token_size and num_sn to destination sizes#1243
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decode_buf() verifies that the source packet still holds the requested number of bytes, but not that the requested length fits the destination buffer. The REGISTER_SUPER / UNREGISTER_SUPER / REGISTER_SUPER_ACK / REGISTER_SUPER_NAK decoders read auth.token_size (a 16-bit field) and num_sn (an 8-bit count) directly from the wire and pass them to decode_buf() targeting fixed-size destinations: auth.token is N2N_AUTH_MAX_TOKEN_SIZE (48) bytes, and the REGISTER_SUPER_ACK backup list is bounded by REG_SUPER_ACK_PAYLOAD_SPACE. A length field larger than its destination therefore lets a malformed packet write past the end of the buffer. Validate token_size against N2N_AUTH_MAX_TOKEN_SIZE and num_sn against REG_SUPER_ACK_PAYLOAD_SPACE before calling decode_buf(), returning a decode error otherwise. A conforming peer never sends a larger value, so well-formed traffic is unaffected. Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
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decode_buf() checks that the source packet holds the requested number of bytes, but not that the requested length fits the destination buffer. The REGISTER_SUPER / UNREGISTER_SUPER / REGISTER_SUPER_ACK / REGISTER_SUPER_NAK decoders read auth.token_size (16-bit) and num_sn (8-bit) directly from the wire and pass them to decode_buf() targeting fixed-size destinations (auth.token is N2N_AUTH_MAX_TOKEN_SIZE = 48 bytes; the backup-supernode list is bounded by REG_SUPER_ACK_PAYLOAD_SPACE).
A length field larger than its destination lets a malformed packet write past the buffer. This validates token_size and num_sn against those limits before the copy and returns a decode error otherwise. Well-formed peers never send larger values, so legitimate traffic is unaffected.
Built clean with -Wall (no new warnings); tools/tests-wire passes.