From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8309DC2BABC for ; Tue, 7 Apr 2020 02:15:37 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 47C7A2076E for ; Tue, 7 Apr 2020 02:15:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="ODXcvNL2" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 47C7A2076E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id D89578E0005; Mon, 6 Apr 2020 22:15:36 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D39A08E0001; Mon, 6 Apr 2020 22:15:36 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BDA2B8E0005; Mon, 6 Apr 2020 22:15:36 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0246.hostedemail.com [216.40.44.246]) by kanga.kvack.org (Postfix) with ESMTP id A0D5A8E0001 for ; Mon, 6 Apr 2020 22:15:36 -0400 (EDT) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 533B2181AEF1A for ; Tue, 7 Apr 2020 02:15:36 +0000 (UTC) X-FDA: 76679442672.11.tail44_6b1994873a835 X-HE-Tag: tail44_6b1994873a835 X-Filterd-Recvd-Size: 3829 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf15.hostedemail.com (Postfix) with ESMTP for ; Tue, 7 Apr 2020 02:15:35 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D26B9206C0; Tue, 7 Apr 2020 02:15:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586225735; bh=/7+kFSdsBEBC6Khz6wgfGcdiDBnwpU8sm/wk9IKrNdY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=ODXcvNL2jbO13NOwHqociXoDhYkqguNgR0GmvcDGbbKd4KCYfAQMA4Fn0hFKfrESP +lDX3yUUD2Z6JXwcm9G+mW/aODZw0tRJj9UFxxCiNaJiZ9YuUXo0dloG9V//CzuU92 kRZkyeDQqICTwKgehE1ygM7VVa2iuRLBa5BiuAeE= Date: Mon, 6 Apr 2020 19:15:34 -0700 From: Andrew Morton To: Peter Xu Cc: syzbot , bgeffon@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, torvalds@linux-foundation.org Subject: Re: BUG: unable to handle kernel paging request in kernel_get_mempolicy Message-Id: <20200406191534.aafd8f74406c242ba1a42549@linux-foundation.org> In-Reply-To: <20200407015535.GC48345@xz-x1> References: <0000000000002b25f105a2a3434d@google.com> <20200407004745.GA48345@xz-x1> <20200406183941.38a2e52026e42dbfde239a56@linux-foundation.org> <20200407015535.GC48345@xz-x1> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, 6 Apr 2020 21:55:35 -0400 Peter Xu wrote: > On Mon, Apr 06, 2020 at 06:39:41PM -0700, Andrew Morton wrote: > > On Mon, 6 Apr 2020 20:47:45 -0400 Peter Xu wrote: > > > > > >From 23800bff6fa346a4e9b3806dc0cfeb74498df757 Mon Sep 17 00:00:00 2001 > > > From: Peter Xu > > > 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? > > It looks ok to me too. I was returning -EFAULT to follow the same > value as get_vaddr_frames() (which is the other caller of > get_user_pages_locked()). So far the only path that I found can > trigger this is when there's a fatal signal pending right after the > gup. If so, the userspace won't have a chance to see the -EINTR (or > whatever we return) anyways. Yup. I guess we're a victim of get_user_pages()'s screwy return value conventions - the caller cannot distinguish between invalid-addr and fatal-signal. Which makes one wonder why lookup_node() ever worked. What happens if get_mempolicy(MPOL_F_NODE) is passed a wild userspace address?