From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx136.postini.com [74.125.245.136]) by kanga.kvack.org (Postfix) with SMTP id 87D586B0002 for ; Mon, 15 Apr 2013 16:58:07 -0400 (EDT) Date: Mon, 15 Apr 2013 13:58:05 -0700 From: Andrew Morton Subject: Re: [PATCH] memcg: Check more strictly to avoid ULLONG overflow by PAGE_ALIGN Message-Id: <20130415135805.c552511917b0dbe113388acb@linux-foundation.org> In-Reply-To: <20130412171108.d3ef3e2d66e9c1bfcf69467c@mxp.nes.nec.co.jp> References: <1365748763-4350-1-git-send-email-handai.szj@taobao.com> <20130412171108.d3ef3e2d66e9c1bfcf69467c@mxp.nes.nec.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Daisuke Nishimura Cc: Sha Zhengju , cgroups@vger.kernel.org, linux-mm@kvack.org, jeff.liu@oracle.com, Sha Zhengju On Fri, 12 Apr 2013 17:11:08 +0900 Daisuke Nishimura wrote: > > --- a/include/linux/res_counter.h > > +++ b/include/linux/res_counter.h > > @@ -54,7 +54,7 @@ struct res_counter { > > struct res_counter *parent; > > }; > > > > -#define RESOURCE_MAX (unsigned long long)LLONG_MAX > > +#define RESOURCE_MAX (unsigned long long)ULLONG_MAX > > > > I don't think it's a good idea to change a user-visible value. The old value was a mistake, surely. RESOURCE_MAX shouldn't be in this header file - that is far too general a name. I suggest the definition be moved to res_counter.c. And the (unsigned long long) cast is surely unneeded if we're to use ULLONG_MAX. > > /** > > * Helpers to interact with userspace > > diff --git a/kernel/res_counter.c b/kernel/res_counter.c > > index ff55247..6c35310 100644 > > --- a/kernel/res_counter.c > > +++ b/kernel/res_counter.c > > @@ -195,6 +195,12 @@ int res_counter_memparse_write_strategy(const char *buf, > > if (*end != '\0') > > return -EINVAL; > > > > - *res = PAGE_ALIGN(*res); > > + /* Since PAGE_ALIGN is aligning up(the next page boundary), > > + * check the left space to avoid overflow to 0. */ > > + if (RESOURCE_MAX - *res < PAGE_SIZE - 1) > > + *res = RESOURCE_MAX; > > + else > > + *res = PAGE_ALIGN(*res); > > + > > Current interface seems strange because we can set a bigger value than > the value which means "unlimited". I'm not sure what you mean by this? > So, how about some thing like: > > if (*res > RESOURCE_MAX) > return -EINVAL; > if (*res > PAGE_ALIGN(RESOURCE_MAX) - PAGE_SIZE) > *res = RESOURCE_MAX; > else > *res = PAGE_ALIGN(*res); > The first thing I'd do to res_counter_memparse_write_strategy() is to rename its second arg to `resp' then add a local called `res'. Because that function dereferences res far too often. Then, - *res = PAGE_ALIGN(*res); if (PAGE_ALIGN(res) >= res) res = PAGE_ALIGN(res); else res = RESOURCE_MAX; /* PAGE_ALIGN wrapped to zero */ *resp = res; return 0; -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org