linux-kernel - Re: [External] Re: [PATCH] mm: memcontrol: Fix out-of-bounds on the buf returned by memory_stat

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Message-ID: <CAMZfGtXd3DNrW5BPjDosHsz-FUYACGZEOAfAYLwyHdRSpOsqhQ@mail.gmail.com>
Date:   Mon, 14 Sep 2020 17:43:42 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Cgroups <cgroups@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [External] Re: [PATCH] mm: memcontrol: Fix out-of-bounds on the
 buf returned by memory_stat_format

On Mon, Sep 14, 2020 at 5:18 PM Michal Hocko <mhocko@...e.com> wrote:
>
> On Mon 14-09-20 12:02:33, Muchun Song wrote:
> > On Sun, Sep 13, 2020 at 8:42 AM Andrew Morton <akpm@...ux-foundation.org> wrote:
> > >
> > > On Sat, 12 Sep 2020 23:51:00 +0800 Muchun Song <songmuchun@...edance.com> wrote:
> > >
> > > > The memory_stat_format() returns a format string, but the return buf
> > > > may not including the trailing '\0'. So the users may read the buf
> > > > out of bounds.
> > >
> > > That sounds serious.  Is a cc:stable appropriate?
> > >
> >
> > Yeah, I think we should cc:stable.
>
> Is this a real problem? The buffer should contain 36 lines which makes
> it more than 100B per line. I strongly suspect we are not able to use
> that storage up.

Before memory_stat_format() return, we should call seq_buf_putc(&s, '\0').
Otherwise, the return buf string has no trailing null('\0'). But users treat buf
as a string(and read the string oob). It is wrong. Thanks.

> --
> Michal Hocko
> SUSE Labs



-- 
Yours,
Muchun