linux-kernel - Re: [PATCH 1/3] kallsyms: don't leak address when symbol not found

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Date:   Tue, 19 Dec 2017 09:41:29 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Felix Fietkau <nbd@....name>, kernel-hardening@...ts.openwall.com
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Tycho Andersen <tycho@...ho.ws>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Alexei Starovoitov <ast@...nel.org>,
        linux-kernel@...r.kernel.org,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/3] kallsyms: don't leak address when symbol not found

On Mon, Dec 18, 2017, at 20:55, Felix Fietkau wrote:
> On 2017-12-18 00:53, Tobin C. Harding wrote:
> > Currently if kallsyms_lookup() fails to find the symbol then the address
> > is printed. This potentially leaks sensitive information. Instead of
> > printing the address we can return an error, giving the calling code the
> > option to print the address or print some sanitized message.
> > 
> > Return error instead of printing address to argument buffer. Leave
> > buffer in a sane state.
> > 
> > Signed-off-by: Tobin C. Harding <me@...in.cc>
> I think there should be a way to keep the old behavior for debugging.

That was the intended use of

EXPORT_SYMBOL(string_is_no_symbol);

in patch 2 of this series. Then if debugging behaviour is adversely
effected one could use string_is_no_symbol() on a case by case basis to
add back in the original behaviour. 

Current suggestion on list is to remove this function. Do you have a use
case in mind where debugging will break? We could add a fix to this
series if so. Otherwise next version will likely drop
string_is_no_symbol()

thanks,
Tobin.