linux-kernel - [PATCH] kasan: avoid overflowing quarantine size on low memory systems

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Message-Id: <1470063563-96266-1-git-send-email-glider@google.com>
Date:	Mon,  1 Aug 2016 16:59:23 +0200
From:	Alexander Potapenko <glider@...gle.com>
To:	dvyukov@...gle.com, kcc@...gle.com, aryabinin@...tuozzo.com,
	adech.fo@...il.com, cl@...ux.com, akpm@...ux-foundation.org,
	rostedt@...dmis.org, js1304@...il.com, iamjoonsoo.kim@....com,
	kuthonuzo.luruo@....com
Cc:	kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [PATCH] kasan: avoid overflowing quarantine size on low memory systems

If the total amount of memory assigned to quarantine is less than the
amount of memory assigned to per-cpu quarantines, |new_quarantine_size|
may overflow. Instead, set it to zero.

Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Fixes: 55834c59098d ("mm: kasan: initial memory quarantine
implementation")
Signed-off-by: Alexander Potapenko <glider@...gle.com>
---
 mm/kasan/quarantine.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index 65793f1..416d3b0 100644
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -196,7 +196,7 @@ void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache)
 
 void quarantine_reduce(void)
 {
-	size_t new_quarantine_size;
+	size_t new_quarantine_size, percpu_quarantines;
 	unsigned long flags;
 	struct qlist_head to_free = QLIST_INIT;
 	size_t size_to_free = 0;
@@ -214,7 +214,15 @@ void quarantine_reduce(void)
 	 */
 	new_quarantine_size = (READ_ONCE(totalram_pages) << PAGE_SHIFT) /
 		QUARANTINE_FRACTION;
-	new_quarantine_size -= QUARANTINE_PERCPU_SIZE * num_online_cpus();
+	percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus();
+	if (new_quarantine_size < percpu_quarantines) {
+		WARN_ONCE(1,
+			"Too little memory, disabling global KASAN quarantine.\n",
+		);
+		new_quarantine_size = 0;
+	} else {
+		new_quarantine_size -= percpu_quarantines;
+	}
 	WRITE_ONCE(quarantine_size, new_quarantine_size);
 
 	last = global_quarantine.head;
-- 
2.8.0.rc3.226.g39d4020