linux-kernel - Re: [PATCH 1/3] mm/vmalloc: fix size check for remap_vmalloc_range

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Message-ID: <20190104102846.GN31793@dhcp22.suse.cz>
Date:   Fri, 4 Jan 2019 11:28:46 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Roman Penyaev <rpenyaev@...e.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Joe Perches <joe@...ches.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 1/3] mm/vmalloc: fix size check for
 remap_vmalloc_range_partial()

On Fri 04-01-19 11:21:39, Roman Penyaev wrote:
> On 2019-01-04 10:38, Michal Hocko wrote:
> 
> [...]
> 
> > > >
> > > > OK, my response was more confusing than I intended. I meant to say. Is
> > > > there any in kernel code that would allow the bug have had in mind?
> > > > In other words can userspace trick any existing code?
> > > 
> > > In theory any existing caller of remap_vmalloc_range() which does
> > > not have an explicit size check should trigger an oops, e.g. this is
> > > a good candidate:
> > > 
> > > *** drivers/media/usb/stkwebcam/stk-webcam.c:
> > > v4l_stk_mmap[789]              ret = remap_vmalloc_range(vma,
> > > sbuf->buffer,
> > > 0);
> > 
> > Hmm, sbuf->buffer is allocated in stk_setup_siobuf to have
> > buf->v4lbuf.length. mmap callback maps this buffer to the vma size and
> > that is indeed not enforced to be <= length AFAICS. So you are right!
> > 
> > Can we have an example in the changelog please?
> 
> You mean to resend this particular patch with the list of possible
> candidates for oops in a comment message?  Sure thing.

I would just reply to the original patch with an updated changelog
wording (to include the above example and explain how the vma setup is
completely independent on the buffer allocation and ask Andrew to update
the changelog of the patch that is already in the mmotm tree).

Thanks!
-- 
Michal Hocko
SUSE Labs