GNU bug report logs - #20087
'gensym' is not guaranteed to return a fresh symbol

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Andy Wingo <wingo <at> pobox.com>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#20087: closed ('gensym' is not guaranteed to return a fresh
 symbol)
Date: Thu, 23 Jun 2016 16:06:02 +0000

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Your message dated Thu, 23 Jun 2016 18:05:30 +0200
with message-id <87bn2roppx.fsf <at> pobox.com>
and subject line Re: bug#20087: gensym
has caused the debbugs.gnu.org bug report #20087,
regarding 'gensym' is not guaranteed to return a fresh symbol
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


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20087: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=20087
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From: ludo <at> gnu.org (Ludovic Courtès)
To: bug-guile <at> gnu.org
Subject: 'gensym' is not guaranteed to return a fresh symbol
Date: Wed, 11 Mar 2015 18:15:02 +0100

‘gensym’ returns interned symbols, but the algorithm to determine the
new symbol is simplistic and predictable.

Thus, one can arrange to produce a symbol before ‘gensym’ does, leading
‘gensym’ to return a symbol that’s not fresh (in terms of ‘eq?’), as is
the case with the second call to ‘gensym’ here:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> (gensym "x")
$1 = x379
scheme@(guile-user)> 'x405
$2 = x405
scheme@(guile-user)> (gensym "x")
$3 = x405
--8<---------------cut here---------------end--------------->8---

Should we worry about it?  I think it may have hard to anticipate
security implications.

Ludo’.

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From: Andy Wingo <wingo <at> pobox.com>
To: ludo <at> gnu.org (Ludovic Courtès)
Cc: Mark H Weaver <mhw <at> netris.org>, 20087-done <at> debbugs.gnu.org,
 rain1 <at> openmailbox.org
Subject: Re: bug#20087: gensym
Date: Thu, 23 Jun 2016 18:05:30 +0200

On Thu 23 Jun 2016 16:13, ludo <at> gnu.org (Ludovic Courtès) writes:

> Andy Wingo <wingo <at> pobox.com> skribis:
>
>> I just pushed something to master to error when serializing an
>> uninterned symbol.  Otherwise compiling an uninterned symbol effectively
>> interns it!  I am not sure that we can apply such a fix in 2.0 though as
>> who knows, maybe someone is compiling something with symbols made with
>> make-symbol.  WDYT?  If you agree we can close this bug.
>
> That makes sense to me.

Closing then.  Thanks for the review :)

Andy

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