linux-kernel - Re: [PATCH 4.9 105/125] mm, gup: add missing refcount overflow checks on x86 and s390

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Date:   Wed, 4 Dec 2019 21:37:11 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Sasha Levin <sashal@...nel.org>,
        Ben Hutchings <ben.hutchings@...ethink.co.uk>
Subject: Re: [PATCH 4.9 105/125] mm, gup: add missing refcount overflow
 checks on x86 and s390

On Wed, Dec 04, 2019 at 07:27:44PM +0100, Vlastimil Babka wrote:
> On 12/4/19 6:56 PM, Greg Kroah-Hartman wrote:
> > From: Vlastimil Babka <vbabka@...e.cz>
> > 
> > The mainline commit 8fde12ca79af ("mm: prevent get_user_pages() from
> > overflowing page refcount") was backported to 4.9.y stable as commit
> > 2ed768cfd895. The backport however missed that in 4.9, there are several
> > arch-specific gup.c versions with fast gup implementations, so these do not
> > prevent refcount overflow.
> > 
> > This is partially fixed for x86 in stable-only commit d73af79742e7 ("x86, mm,
> > gup: prevent get_page() race with munmap in paravirt guest"). This stable-only
> > commit adds missing parts to x86 version, as well as s390 version, both taken
> > from the SUSE SLES/openSUSE 4.12-based kernels.
> > 
> > The remaining architectures with own gup.c are sparc, mips, sh. It's unlikely
> > the known overflow scenario based on FUSE, which needs 140GB of RAM, is a
> > problem for those architectures, and I don't feel confident enough to patch
> > them.
> > 
> > Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> > Signed-off-by: Sasha Levin <sashal@...nel.org>
> 
> No, this one had a leak bug and I've sent updated version:
> https://lore.kernel.org/linux-mm/e274291b-054f-2fad-28e8-59fabf312e61@suse.cz/

Ugh.  Ok, let me go fix that up...