From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id 258DE8D0039 for ; Thu, 17 Feb 2011 21:21:32 -0500 (EST) Message-ID: <4D5DD7F9.30202@cn.fujitsu.com> Date: Fri, 18 Feb 2011 10:22:49 +0800 From: Li Zefan MIME-Version: 1.0 Subject: Re: [PATCH 1/4] cpuset: Remove unneeded NODEMASK_ALLOC() in cpuset_sprintf_memlist() References: <4D5C7EA7.1030409@cn.fujitsu.com> In-Reply-To: Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Paul Menage Cc: Andrew Morton , LKML , David Rientjes , =?UTF-8?B?57yqIOWLsA==?= , linux-mm@kvack.org Paul Menage wrote: > On Wed, Feb 16, 2011 at 5:49 PM, Li Zefan wrote: >> It's not necessary to copy cpuset->mems_allowed to a buffer >> allocated by NODEMASK_ALLOC(). Just pass it to nodelist_scnprintf(). >> >> Signed-off-by: Li Zefan > > Acked-by: Paul Menage > > The only downside is that we're now doing more work (and more complex > work) inside callback_mutex, but I guess that's OK compared to having > to do a memory allocation. (I poked around in lib/vsprintf.c and I > couldn't see any cases where it might allocate memory, but it would be > particularly bad if there was any way to trigger an Oops.) > >> --- >> kernel/cpuset.c | 10 +--------- >> 1 files changed, 1 insertions(+), 9 deletions(-) >> >> diff --git a/kernel/cpuset.c b/kernel/cpuset.c >> index 10f1835..f13ff2e 100644 >> --- a/kernel/cpuset.c >> +++ b/kernel/cpuset.c >> @@ -1620,20 +1620,12 @@ static int cpuset_sprintf_cpulist(char *page, struct cpuset *cs) >> >> static int cpuset_sprintf_memlist(char *page, struct cpuset *cs) >> { >> - NODEMASK_ALLOC(nodemask_t, mask, GFP_KERNEL); >> int retval; >> >> - if (mask == NULL) >> - return -ENOMEM; >> - > > And this was particularly broken since the only caller of > cpuset_sprintf_memlist() doesn't handle a negative error response > anyway and would then overwrite byte 4083 on the preceding page with a > '\n'. And then since the (size_t)(s-page) that's passed to > simple_read_from_buffer() would be a very large number, it would write > arbitrary (user-controlled) amounts of kernel data to the userspace > buffer. > > Maybe we could also rename 'retval' to 'count' in this function (and > cpuset_sprintf_cpulist()) to make it clearer that callers don't expect > negative error values? > Good spot! -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org