[COFF] [TUHS] buffer overflow (Re: Happy birthday Morris worm

[peter at rulingia.com (Peter Jeremy)]

On 2019-Nov-12 17:49:46 -0500, Arthur Krewat <krewat at kilonet.net> wrote:
>On 11/12/2019 5:41 PM, Robert Clausecker wrote:
>> Oh please no.  One of the things we've hopefully all learned from Pascal
>> is that length-prefixed strings suck because you can't perform anything
>> useful without copying the entire string.

Keep in mind that C doesn't have a "string" type.  The use of a NUL
terminated char array is purely convention.  There's nothing to stop
someone using a length-prefixed array (though there's virtually no
standard library support for that).

>> Rob Pike and friends showed
>> how to get strings and vectors right in the Go language where you have a
>> builtin slice type which is essentially a structure
>>
>>      struct slice(type) {
>>              type *data;
>>              size_t len, cap;
>>      };

That approach would have incurred a 12-byte overhead for each string or
vector on a PDP-11 - that would have been a substantial disincentive on
a memory-constrained system.

>And none of that stops some programmer from doing slice.cap=255 - or is 
>it read-only? ;)

Slices and strings are built-in types in Go.  They can be modelled as the
above structure but that is an implementation detail.  It is possible to
reduce the capacity of a slice (but not a string) but attempting to
increase it will result in a runtime exception ("panic" in Go speak).

-- 
Peter Jeremy
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