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From: Al Viro <viro@ZenIV.linux.org.uk>
To: Kees Cook <keescook@chromium.org>
Cc: linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Josh Triplett <josh@joshtriplett.org>,
	Serge Hallyn <serge.hallyn@canonical.com>,
	linux-fsdevel@vger.kernel.org, halfdog <me@halfdog.net>
Subject: Re: [PATCH] exec: do not leave bprm->interp on stack
Date: Thu, 25 Oct 2012 05:16:21 +0100	[thread overview]
Message-ID: <20121025041620.GH2616@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20121024232032.GA31129@www.outflux.net>

On Wed, Oct 24, 2012 at 04:20:32PM -0700, Kees Cook wrote:
> If a series of scripts are executed, each triggering module loading via
> unprintable bytes in the script header, kernel stack contents can leak
> into the command line.
> 
> Normally execution of binfmt_script and binfmt_misc happens
> recursively. However, when modules are enabled, and unprintable bytes
> exist in the bprm->buf, execution will restart after attempting to load
> matching binfmt modules. Unfortunately, the logic in binfmt_script and
> binfmt_misc does not expect to get restarted. They leave bprm->interp
> pointing to their local stack. This means on restart bprm->interp is
> left pointing into unused stack memory which can then be copied into
> the userspace argv areas.
> 
> This changes the logic to require allocation for any changes to the
> bprm->interp. To avoid adding a new kmalloc to every exec, the default
> value is left as-is. Only when passing through binfmt_script or
> binfmt_misc does an allocation take place.

I really don't like that.  It papers over the problem, but doesn't really
solve the underlying stupidity.  We have no good reason to retry a binfmt
we'd already attempted on this level of recursion.  And your patch doesn't
deal with that at all.

  reply	other threads:[~2012-10-25  4:16 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-10-24 23:20 [PATCH] exec: do not leave bprm->interp on stack Kees Cook
2012-10-25  4:16 ` Al Viro [this message]
2012-10-25  6:21   ` Kees Cook
2012-10-25 11:46     ` P J P
2012-10-25 12:03       ` Tetsuo Handa
2012-10-25 12:57         ` P J P
2012-10-25 12:09       ` Al Viro
2012-10-25 12:38         ` Al Viro
2012-10-26 17:38           ` P J P
2012-10-26 18:36             ` Al Viro
2012-10-27 10:47               ` P J P
2012-10-27 17:05                 ` Kees Cook
2012-10-27 20:16                   ` P J P
2012-10-28  3:32                     ` Kees Cook
2012-11-06  8:10                       ` P J P
2012-11-12 22:10                         ` Kees Cook
2012-11-13  6:50                           ` halfdog
2012-11-16 12:50                           ` P J P
2012-11-16 18:00                             ` Kees Cook
2012-11-18 19:04                               ` P J P
2012-11-18 19:34                                 ` Kees Cook
2012-11-19  6:57                                   ` P J P
2012-11-19 20:41                                     ` Kees Cook
2012-11-20  7:04                                       ` P J P
2012-11-22 20:06                                       ` P J P
2012-11-23 18:43                                       ` P J P
2012-11-23 23:12                                         ` Tetsuo Handa
     [not found]                                       ` <alpine.LFD.2.02.1211221934220.19768@wniryva.cad.erqung.pbz>
     [not found]                                         ` <CAGXu5jL8zCt5ghW4ODPL9+SyC9+mbuw=4JMUngepY5fC8pSikQ@mail.gmail.com>
2012-11-26  7:09                                           ` P J P
     [not found]                                     ` <CA+55aFx3LFH5Xj1OkNoy7vN5w8y5tH39MUDujKqF3BdnmYibLQ@mail.gmail.com>
2012-11-20  7:08                                       ` P J P

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