linux-kernel - Re: [PATCH] mm/sparse:avoid null pointer access in memory

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CACZJ9cWFyr7MyGWWaGiNYHDb39ZYAmijH90gAH5N8-z4jc2KNw@mail.gmail.com>
Date:   Sat, 17 Jun 2023 16:59:46 +0800
From:   Liam Ni <zhiguangni01@...il.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm/sparse:avoid null pointer access in memory_present()

On Sat, 17 Jun 2023 at 15:01, Mike Rapoport <rppt@...nel.org> wrote:
>
> On Sat, Jun 17, 2023 at 02:17:58PM +0800, Liam Ni wrote:
> > On Sat, 17 Jun 2023 at 13:44, Andrew Morton <akpm@...ux-foundation.org> wrote:
> > >
> > > On Sat, 17 Jun 2023 14:40:36 +1000 Liam Ni <zhiguangni01@...il.com> wrote:
> > >
> > > > __nr_to_section() may return a null pointer,
> > > > before accessing the member variable section_mem_map,
> > > > we should first determine whether it is a null pointer.
> > > >
> > > > ...
> > > >
> > > > --- a/mm/sparse.c
> > > > +++ b/mm/sparse.c
> > > > @@ -258,7 +258,7 @@ static void __init memory_present(int nid, unsigned long start, unsigned long en
> > > >               set_section_nid(section, nid);
> > > >
> > > >               ms = __nr_to_section(section);
> > > > -             if (!ms->section_mem_map) {
> > > > +             if (ms && !ms->section_mem_map) {
> > > >                       ms->section_mem_map = sparse_encode_early_nid(nid) |
> > > >                                                       SECTION_IS_ONLINE;
> > > >                       __section_mark_present(ms, section);
> > >
> > > I'm suspecting that if __nr_to_section() returns NULL here, we should
> > > just panic.  But a null-deref gives the same information, so why change
> > > things?
> >
> > Do you mean if ms is a null pointer，ms->section_mem_map will cause
> > system panic,so we needn't change?
>
> Yes, if __nr_to_section ever returns NULL the system will crash anyway.

I got it,do we need to print some information by panic()?

>
> --
> Sincerely yours,
> Mike.