RFR: 8264948: Check for TLS extensions total length

[Jamil Nimeh]

On Fri, 9 Apr 2021 04:55:14 GMT, Xue-Lei Andrew Fan <xuelei at openjdk.org> wrote:

> To improve the readability, it would be nice to check the TLS extensions total length while parsing.
> 
> No new regression test,  trial update.

src/java.base/share/classes/sun/security/ssl/SSLExtensions.java line 68:

> 66:                     Alert.ILLEGAL_PARAMETER,
> 67:                     "Insufficient extensions data");
> 68:         }

For both of these blocks the checks themselves look OK, but illegal_parameter I thought was more for cases where a field value is out of range or inconsistent with already negotiated parameters.  I would think that decode_error would be more appropriate to cases like this where the encoding is structurally incorrect and the length doesn't match the actual data size.

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PR: https://git.openjdk.java.net/jdk/pull/3405