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From 00fc586ea7410ee8664bfd4f4ea246c60ea0482c Mon Sep 17 00:00:00 2001
From: Yisheng Xie <xieyisheng1@huawei.com>
Date: Fri, 2 Jun 2017 14:46:43 -0700
Subject: [PATCH] mlock: fix mlock count can not decrease in race condition
[ Upstream commit 70feee0e1ef331b22cc51f383d532a0d043fbdcc ]
Kefeng reported that when running the follow test, the mlock count in
meminfo will increase permanently:
[1] testcase
linux:~ # cat test_mlockal
grep Mlocked /proc/meminfo
for j in `seq 0 10`
do
for i in `seq 4 15`
do
./p_mlockall >> log &
done
sleep 0.2
done
# wait some time to let mlock counter decrease and 5s may not enough
sleep 5
grep Mlocked /proc/meminfo
linux:~ # cat p_mlockall.c
#include <sys/mman.h>
#include <stdlib.h>
#include <stdio.h>
#define SPACE_LEN 4096
int main(int argc, char ** argv)
{
int ret;
void *adr = malloc(SPACE_LEN);
if (!adr)
return -1;
ret = mlockall(MCL_CURRENT | MCL_FUTURE);
printf("mlcokall ret = %d\n", ret);
ret = munlockall();
printf("munlcokall ret = %d\n", ret);
free(adr);
return 0;
}
In __munlock_pagevec() we should decrement NR_MLOCK for each page where
we clear the PageMlocked flag. Commit 1ebb7cc6a583 ("mm: munlock: batch
NR_MLOCK zone state updates") has introduced a bug where we don't
decrement NR_MLOCK for pages where we clear the flag, but fail to
isolate them from the lru list (e.g. when the pages are on some other
cpu's percpu pagevec). Since PageMlocked stays cleared, the NR_MLOCK
accounting gets permanently disrupted by this.
Fix it by counting the number of page whose PageMlock flag is cleared.
Fixes: 1ebb7cc6a583 (" mm: munlock: batch NR_MLOCK zone state updates")
Link: http://lkml.kernel.org/r/1495678405-54569-1-git-send-email-xieyisheng1@huawei.com
CVE: CVE-2017-18221
Upstream-Status: Backport
Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com>
Reported-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Joern Engel <joern@logfs.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michel Lespinasse <walken@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Xishi Qiu <qiuxishi@huawei.com>
Cc: zhongjiang <zhongjiang@huawei.com>
Cc: Hanjun Guo <guohanjun@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Andreas Wellving <andreas.wellving@enea.com>
---
mm/mlock.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/mm/mlock.c b/mm/mlock.c
index 3d3ee6ca..00ff8c7 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -277,7 +277,7 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
{
int i;
int nr = pagevec_count(pvec);
- int delta_munlocked;
+ int delta_munlocked = -nr;
struct pagevec pvec_putback;
int pgrescued = 0;
@@ -297,6 +297,8 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
continue;
else
__munlock_isolation_failed(page);
+ } else {
+ delta_munlocked++;
}
/*
@@ -308,7 +310,6 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
pagevec_add(&pvec_putback, pvec->pages[i]);
pvec->pages[i] = NULL;
}
- delta_munlocked = -nr + pagevec_count(&pvec_putback);
__mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);
spin_unlock_irq(&zone->lru_lock);
--
2.7.4
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