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 16:44:03 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Linux Kernel <linux-kernel@...r.kernel.org>
Cc:     chianglungyu@...il.com, Janis Danisevskis <jdanis@...gle.com>,
        John Stultz <john.stultz@...aro.org>,
        Kees Cook <keescook@...omium.org>,
        Mateusz Guzik <mguzik@...hat.com>, mhocko@...e.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, 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() ?