linux-kernel - Re: BUG: unable to handle kernel paging request in kernel_get

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Date:   Mon, 6 Apr 2020 18:39:41 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Peter Xu <peterx@...hat.com>
Cc:     syzbot <syzbot+693dc11fcb53120b5559@...kaller.appspotmail.com>,
        bgeffon@...gle.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, syzkaller-bugs@...glegroups.com,
        torvalds@...ux-foundation.org
Subject: Re: BUG: unable to handle kernel paging request in
 kernel_get_mempolicy

On Mon, 6 Apr 2020 20:47:45 -0400 Peter Xu <peterx@...hat.com> wrote:

> >From 23800bff6fa346a4e9b3806dc0cfeb74498df757 Mon Sep 17 00:00:00 2001
> From: Peter Xu <peterx@...hat.com>
> Date: Mon, 6 Apr 2020 20:40:13 -0400
> Subject: [PATCH] mm/mempolicy: Allow lookup_node() to handle fatal signal
> 
> lookup_node() uses gup to pin the page and get node information.  It
> checks against ret>=0 assuming the page will be filled in.  However
> it's also possible that gup will return zero, for example, when the
> thread is quickly killed with a fatal signal.  Teach lookup_node() to
> gracefully return an error -EFAULT if it happens.
> 
> ...
>
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -902,7 +902,10 @@ static int lookup_node(struct mm_struct *mm, unsigned long addr)
>  
>  	int locked = 1;
>  	err = get_user_pages_locked(addr & PAGE_MASK, 1, 0, &p, &locked);
> -	if (err >= 0) {
> +	if (err == 0) {
> +		/* E.g. GUP interupted by fatal signal */
> +		err = -EFAULT;
> +	} else if (err > 0) {
>  		err = page_to_nid(p);
>  		put_page(p);
>  	}

Doh.  Thanks.

Should it have been -EINTR?