linux-kernel - Re: [PATCH 0/5] kallsyms: make kallsym APIs more safe with scnprintf

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Date:   Wed, 15 Jun 2022 10:01:57 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Maninder Singh <maninder1.s@...sung.com>, bcain@...cinc.com,
        mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
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Subject: Re: [PATCH 0/5] kallsyms: make kallsym APIs more safe with scnprintf

On Mon 2022-05-23 12:39:12, Kees Cook wrote:
> On Sat, May 21, 2022 at 11:07:52PM -0700, Christoph Hellwig wrote:
> > On Fri, May 20, 2022 at 02:06:56PM +0530, Maninder Singh wrote:
> > > kallsyms functionality depends on KSYM_NAME_LEN directly.
> > > but if user passed array length lesser than it, sprintf
> > > can cause issues of buffer overflow attack.
> > > 
> > > So changing *sprint* and *lookup* APIs in this patch set
> > > to have buffer size as an argument and replacing sprintf with
> > > scnprintf.
> > 
> > This is still a pretty horrible API.  Passing something like
> > a struct seq_buf seems like the much better API here.  Also with
> > the amount of arguments and by reference passing it might be worth
> > to pass them as a structure while you're at it.
> 
> Yeah, I agree. It really seems like seq_buf would be nicer.

There is a new patchset that is trying to use this kind of buffer
in vsprintf.

It introduces another buffer struct because vsprintf() needs a bit
different semantic than the one used in seq_buf. But it actually
replaces seq_buf() in the end. I am not sure if this is the right
approach.

Anyway, the initial API is very simple, see
https://lore.kernel.org/r/20220604193042.1674951-2-kent.overstreet@gmail.com

And it makes the internal vsprintf() API more sane, see
https://lore.kernel.org/r/20220604193042.1674951-4-kent.overstreet@gmail.com

It would eventually solve also concerns about the kallsysms API.
Any comments on the new printbuf API are much appreaciated.

Best Regards,
Petr