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 [thread overview]
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 I don't like that comments in OOM code is outdated.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
next prev parent reply other threads:[~2018-11-09 9:56 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-09 4:09 UBSAN: Undefined behaviour in mm/page_alloc.c 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
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