linux-kernel - Re: + proc-fix-null-dereference-when-reading-proc-pid-auxv.patch added to -mm tree

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Date:   Fri, 21 Oct 2016 16:14:54 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     Linux Kernel <linux-kernel@...r.kernel.org>,
        chianglungyu@...il.com, Janis Danisevskis <jdanis@...gle.com>,
        John Stultz <john.stultz@...aro.org>,
        Kees Cook <keescook@...omium.org>,
        Mateusz Guzik <mguzik@...hat.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>, mm-commits@...r.kernel.org
Subject: Re: + proc-fix-null-dereference-when-reading-proc-pid-auxv.patch
 added to -mm tree

On Fri 21-10-16 16:44:03, Alexey Dobriyan wrote:
> On Fri, Oct 21, 2016 at 6:13 AM,  <akpm@...ux-foundation.org> wrote:
> 
> > Reading auxv of any kernel thread results in NULL pointer dereferencing in
> > auxv_read() where mm can be NULL.  Fix that by checking for NULL mm and
> > bailing out early.  This is also the original behavior changed by recent
> > commit c5317167854e ("proc: switch auxv to use of __mem_open()").
> 
> > --- a/fs/proc/base.c~proc-fix-null-dereference-when-reading-proc-pid-auxv
> > +++ a/fs/proc/base.c
> > @@ -1014,6 +1014,9 @@ static ssize_t auxv_read(struct file *fi
> >  {
> >         struct mm_struct *mm = file->private_data;
> >         unsigned int nwords = 0;
> > +
> > +       if (!mm)
> > +               return 0;
> 
> Rhetorical question: who wrote such clever __mem_open() ?

This is nothing really new. __mem_open resp. proc_mem_open returned NULL
mm for ages. I was suggesting to return ESRCH for NULL mm [1].

[1] http://lkml.kernel.org/r/20161019171748.GO24393@dhcp22.suse.cz

-- 
Michal Hocko
SUSE Labs