Linux-mm Archive on lore.kernel.org
 help / color / Atom feed
From: Michal Hocko <mhocko@kernel.org>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Kyungtae Kim <kt0755@gmail.com>,
	akpm@linux-foundation.org, pavel.tatashin@microsoft.com,
	vbabka@suse.cz, osalvador@suse.de, rppt@linux.vnet.ibm.com,
	aaron.lu@intel.com, iamjoonsoo.kim@lge.com,
	alexander.h.duyck@linux.intel.com, mgorman@techsingularity.net,
	lifeasageek@gmail.com, threeearcat@gmail.com,
	syzkaller@googlegroups.com, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org,
	Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Subject: Re: UBSAN: Undefined behaviour in mm/page_alloc.c
Date: Fri, 9 Nov 2018 10:56:04 +0100
Message-ID: <20181109095604.GC5321@dhcp22.suse.cz> (raw)
In-Reply-To: <b51aae15-eb5d-47f0-1222-bfc1ef21e06c@I-love.SAKURA.ne.jp>

On Fri 09-11-18 18:41:53, Tetsuo Handa wrote:
> On 2018/11/09 17:43, Michal Hocko wrote:
> > @@ -4364,6 +4353,17 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, int preferred_nid,
> >  	gfp_t alloc_mask; /* The gfp_t that was actually used for allocation */
> >  	struct alloc_context ac = { };
> >  
> > +	/*
> > +	 * In the slowpath, we sanity check order to avoid ever trying to
> 
> Please keep the comment up to dated.

Does this following look better?

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9fc10a1029cf..bf9aecba4222 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4354,10 +4354,8 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, int preferred_nid,
 	struct alloc_context ac = { };
 
 	/*
-	 * In the slowpath, we sanity check order to avoid ever trying to
-	 * reclaim >= MAX_ORDER areas which will never succeed. Callers may
-	 * be using allocators in order of preference for an area that is
-	 * too large.
+	 * There are several places where we assume that the order value is sane
+	 * so bail out early if the request is out of bound.
 	 */
 	if (order >= MAX_ORDER) {
 		WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN));

> I don't like that comments in OOM code is outdated.
> 
> > +	 * reclaim >= MAX_ORDER areas which will never succeed. Callers may
> > +	 * be using allocators in order of preference for an area that is
> > +	 * too large.
> > +	 */
> > +	if (order >= MAX_ORDER) {
> 
> Also, why not to add BUG_ON(gfp_mask & __GFP_NOFAIL); here?

Because we do not want to blow up the kernel just because of a stupid
usage of the allocator. Can you think of an example where it would
actually make any sense?

I would argue that such a theoretical abuse would blow up on an
unchecked NULL ptr access. Isn't that enough?
-- 
Michal Hocko
SUSE Labs

  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-09  4:09 Kyungtae Kim
2018-11-09  8:42 ` Vlastimil Babka
2018-11-09  8:43 ` Michal Hocko
2018-11-09  9:41   ` Tetsuo Handa
2018-11-09  9:56     ` Michal Hocko [this message]
2018-11-09 10:07       ` Tetsuo Handa
2018-11-09 10:25         ` Michal Hocko
2018-11-09 10:10       ` Vlastimil Babka
2018-11-09 10:22         ` Michal Hocko
2018-11-09 10:24         ` Tetsuo Handa
2018-11-09 10:28           ` Michal Hocko
2018-11-09 10:52       ` Balbir Singh
2018-11-09  9:56   ` Mel Gorman
2018-11-13  9:43   ` Michal Hocko
2018-11-13 23:15     ` Andrew Morton
2018-11-13 23:23       ` Vlastimil Babka
2018-11-13 23:32         ` Andrew Morton
2018-11-14  0:05           ` Vlastimil Babka
2018-11-19 23:57             ` Pavel Machek
2018-11-13 23:29     ` Andrew Morton
2018-11-14  7:10       ` Michal Hocko
2018-11-16 23:43       ` Dmitry Vyukov

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20181109095604.GC5321@dhcp22.suse.cz \
    --to=mhocko@kernel.org \
    --cc=aaron.lu@intel.com \
    --cc=akpm@linux-foundation.org \
    --cc=alexander.h.duyck@linux.intel.com \
    --cc=iamjoonsoo.kim@lge.com \
    --cc=khlebnikov@yandex-team.ru \
    --cc=kt0755@gmail.com \
    --cc=lifeasageek@gmail.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mgorman@techsingularity.net \
    --cc=osalvador@suse.de \
    --cc=pavel.tatashin@microsoft.com \
    --cc=penguin-kernel@I-love.SAKURA.ne.jp \
    --cc=rppt@linux.vnet.ibm.com \
    --cc=syzkaller@googlegroups.com \
    --cc=threeearcat@gmail.com \
    --cc=vbabka@suse.cz \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-mm Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mm/0 linux-mm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mm linux-mm/ https://lore.kernel.org/linux-mm \
		linux-mm@kvack.org
	public-inbox-index linux-mm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kvack.linux-mm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git