Re: [PATCH] introduce CONFIG_BINFMT_ELF_AOUT

Marcelo Tosatti
2006-08-21T00:14:30Z

On Sun, Aug 20, 2006 at 03:25:56AM +0400, Solar Designer wrote:
> Willy,
>
> I propose the attached patch (extracted from 2.4.33-ow1) for inclusion
> into 2.4.34-pre. (2.6 kernels could benefit from the same change, too.)
>
> The patch adds a new compile-time option to control the support for
> "ELF binaries with a.out format interpreters or a.out libraries".
> Without this patch, such support is enabled on every system that enables
> the support for ELF binaries - although 99% (100%?) of systems don't
> need this hybrid functionality. Moreover, this functionality poses a
> security risk - as proven in practice:
>
> http://www.isec.pl/vulnerabilities/isec-0021-uselib.txt
>
> This uselib() vulnerability did not affect default kernel builds with
> the -ow patch specifically due to separation of the unneeded/risky code
> into CONFIG_BINFMT_ELF_AOUT and having this option disabled by default.
> (Yes, this change in -ow patches pre-dates the discovery of the uselib()
> vulnerability.)
>
> The patch also changes CONFIG_BINFMT_AOUT to be disabled by default on
> archs that had it default to enabled. The a.out support is similarly
> risky and not audited/hardened with the same scrutiny that the ELF
> support has received.

I dislike this change. "Make a.out configurable" is a:

- "Hide the problems" trick, making it less likely for any potential bug to
be really fixed.

- Change not suitable for v2.4 inclusion: its not fixing _any_ serious problem.

We had this discussion before, didnt we?