linux-kernel - Re: [PATCH 1/2] mm/mempolicy: Allow lookup

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Message-ID: <20200408102128.GX18914@dhcp22.suse.cz>
Date:   Wed, 8 Apr 2020 12:21:28 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        syzbot+693dc11fcb53120b5559@...kaller.appspotmail.com
Subject: Re: [PATCH 1/2] mm/mempolicy: Allow lookup_node() to handle fatal
 signal

On Tue 07-04-20 21:40:09, Peter Xu wrote:
> 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.
> 
> Meanwhile, initialize "page" to NULL to avoid potential risk of
> exploiting the pointer.
> 
> Reported-by: syzbot+693dc11fcb53120b5559@...kaller.appspotmail.com
> Fixes: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple times")

I am not familiar with thic commit but shouldn't gup return ERESTARTSYS
on a fatal signal?
-- 
Michal Hocko
SUSE Labs