linux-kernel - Re: [RFC 0/3] kallsyms: don't leak address when printing symbol

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Date:   Mon, 27 Nov 2017 16:52:21 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "Tobin C. Harding" <me@...in.cc>
Cc:     kernel-hardening@...ts.openwall.com,
        LKML <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tycho Andersen <tycho@...ho.ws>
Subject: Re: [RFC 0/3] kallsyms: don't leak address when printing symbol

On Mon, Nov 27, 2017 at 2:30 PM, Tobin C. Harding <me@...in.cc> wrote:
> This is an RFC for two reasons.
>
> 1) I don't know who this patch set may break?
> 2) Patch set includes a function that is not called. Function is there
>    to facilitate fixing breakages.
>
> _If_ no one gets broken then we can remove the unused function.
>
> Thanks for looking at this.
>
> Currently if a pointer is printed using %p[ssB] and the symbol is not
> found (kallsyms_lookup() fails) then we print the actual address. This
> potentially leaks kernel addresses. We could instead print something
> _safe_. If kallsyms is made to return an error then callers of
> sprint_symbol() can decide what to do.
>
> In the case of vsprintf we can print '<no-symbol>' (patch 2).
>
> In the case of trace we want the address so we can check the return code
> and print the address if no symbol is found (patch 3).
>
> Design for this set loosely suggested by Steve Rostedt (so as not to
> break ftrace).

If tracing is the only place this is needed, this series seems reasonable to me.

-Kees

>
>
> Patch 1 and 2 tested, patch 3 (trace stuff) untested :)
>
> thanks,
> Tobin.
>
> Tobin C. Harding (3):
>   kallsyms: don't leak address when symbol not found
>   vsprintf: print <no-symbol> if symbol not found
>   trace: print address if symbol not found
>
>  include/linux/kernel.h           |  2 ++
>  kernel/kallsyms.c                |  6 ++++--
>  kernel/trace/trace.h             | 24 ++++++++++++++++++++++++
>  kernel/trace/trace_events_hist.c |  6 +++---
>  lib/vsprintf.c                   | 18 +++++++++++++++---
>  5 files changed, 48 insertions(+), 8 deletions(-)
>
> --
> 2.7.4
>



-- 
Kees Cook
Pixel Security