linux-kernel - Re: [PATCH] fs/binfmt_elf.c: allocate initialized memory in fill_thread_core

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Message-ID: <CAG_fn=X_eQ4G-0+oAO_q+_zRnkfMf4uhfMcnoYt4i1N_noKgdA@mail.gmail.com>
Date:   Tue, 21 Apr 2020 14:54:23 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, sunhaoyl@...look.com
Subject: Re: [PATCH] fs/binfmt_elf.c: allocate initialized memory in fill_thread_core_info()

On Tue, Apr 21, 2020 at 5:42 AM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Mon, Apr 20, 2020 at 03:41:40PM -0700, Kees Cook wrote:
> > On Mon, Apr 20, 2020 at 03:33:52PM -0700, Andrew Morton wrote:
> > > On Sun, 19 Apr 2020 12:08:48 +0200 glider@...gle.com wrote:
> > >
> > > > KMSAN reported uninitialized data being written to disk when dumping
> > > > core. As a result, several kilobytes of kmalloc memory may be written to
> > > > the core file and then read by a non-privileged user.
> >
> > Ewww. That's been there for 12 years. Did something change in
> > regset_size() or regset->get()? Do you know what leaves the hole?
>
> Not lately and I would also like to hear the details; which regset it is?
> Should be reasonably easy to find - just memset() the damn thing to something
> recognizable, do whatever triggers that KMSAN report and look at that
> resulting coredump.
>

Seems to be REGSET_XSTATE filled by xstateregs_get().
Is there a ptrace interface also using that function?

-- 
Alexander Potapenko
Software Engineer

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