linux-kernel - Re: [PATCH 0/3] Unexport kallsyms_lookup_name() and kallsyms_on_each

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Message-ID: <20200302193957.GA276441@kroah.com>
Date:   Mon, 2 Mar 2020 20:39:57 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com, akpm@...ux-foundation.org,
        "K . Prasad" <prasad@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Frederic Weisbecker <frederic@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Quentin Perret <qperret@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>, rostedt@...dmis.org
Subject: Re: [PATCH 0/3] Unexport kallsyms_lookup_name() and
 kallsyms_on_each_symbol()

On Mon, Mar 02, 2020 at 08:36:58PM +0100, Greg Kroah-Hartman wrote:
> On Mon, Mar 02, 2020 at 02:28:11PM -0500, Mathieu Desnoyers wrote:
> > On 21-Feb-2020 11:44:01 AM, Will Deacon wrote:
> > > Hi folks,
> > > 
> > > Despite having just a single modular in-tree user that I could spot,
> > > kallsyms_lookup_name() is exported to modules and provides a mechanism
> > > for out-of-tree modules to access and invoke arbitrary, non-exported
> > > kernel symbols when kallsyms is enabled.
> > > 
> > > This patch series fixes up that one user and unexports the symbol along
> > > with kallsyms_on_each_symbol(), since that could also be abused in a
> > > similar manner.
> > 
> > Hi,
> > 
> > I maintain a GPL kernel tracer (LTTng) since 2005 which happens to be
> > out-of-tree, even though we have made unsuccessful attempts to upstream
> > it in the past. It uses kallsyms_lookup_name() to fetch a few symbols. I
> > would be very glad to have them GPL-exported upstream rather than
> > relying on this work-around. Here is the list of symbols we would need
> > to GPL-export:
> > 
> > stack_trace_save
> > stack_trace_save_user
> > vmalloc_sync_all (CONFIG_X86)
> > get_pfnblock_flags_mask
> > disk_name
> > block_class
> > disk_type
> 
> I hate to ask, but why does anyone need block_class?  or disk_name or
> disk_type?  I need to put them behind a driver core namespace or
> something soon...

Wait, disk_type is a static variable.  And there's multiple ones of
them, how does that work?

thanks,

greg k-h