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Date: Fri, 10 May 2013 12:53:12 +0200
Message-ID: <CAH-PCH5mWuhF84zUvyRamtcv35=c8SZ9XMzutAL3BzqtHJp4tw@mail.gmail.com>
To: Etienne Kneuss <colder@php.net>
Cc: Rasmus Schultz <me@rasmus-schultz.com>, PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] exceptions during __toString()
From: tyra3l@gmail.com (Ferenc Kovacs)

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On Fri, May 10, 2013 at 12:50 AM, Etienne Kneuss <colder@php.net> wrote:

> On Fri, May 10, 2013 at 12:00 AM, Rasmus Schultz <me@rasmus-schultz.com
> >wrote:
>
> > I just ran into this issue again:
> >
> >
> >
> http://stackoverflow.com/questions/2429642/why-its-impossible-to-throw-ex=
ception-from-tostring
> >
> > Instead of throwing some nonsense "you're not allowed to throw from her=
e"
> > error-message, how about actually unwinding the stack and passing the
> > exception to the global exception-handler?
> >
> > I understand there's a technical limitation making it
> difficult/impossible
> > to handle exceptions during __toString() - and it looks like you can
> still
> > try {...} catch (Exception $e) in __toString() just fine, but then what=
?
> > You have the exception, but you have no way to pass it to the standard
> > global exception-handler.
> >
> > If the script has to terminate either way, why not terminate the same w=
ay
> > an unhandled exception would normally cause the script to terminate?
> >
> > E.g. output the actual error-message, or pass it to whatever was
> registered
> > with register_exception_handler() so it can be output or handled in the
> > usual way?
> >
>
>
> The reason is that toString can be triggered from a lot of internal place=
s.
> If an exception is thrown and caught within toString, it's not a problem.
> The problem is if the exception escapes toString, because it thus means
> that the code invoking toString must be interrupted.
>
> We in fact have no guarantee that all those internal places will work
> consistently/correctly in the presence of an exception, and if the engine
> will remain in a state that allows executing code afterward.
> Not executing code means we need to bypass error handlers as well.
>
> Handling an exception from internal code is a "manual" procedure, and cod=
e
> written that relies on conversions to strings may not have been written
> with support for exceptions in mind.
>
> I guess the alternative approach is to allow exceptions, review the code
> (i.e. a lot of work), and eventually fix reports as they come in.
>
> Best,
>
> --
> Etienne Kneuss
>

if somebody thinks that these kind of vulnerabilities are hypotetical, we
had a bunch of Interruption Vulnerabilities in the past and this could
potentionally introduce a lot more, but I think that this is something that
we have to resolve sooner or later, otherwise a whole bunch of proposed
features can never be introduced (for example accepting ArrayObjects
everywhere where array is accepted).

--=20
Ferenc Kov=C3=A1cs
@Tyr43l - http://tyrael.hu

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