[Devel] [PATCH RHEL7 COMMIT] kasan: avoid overflowing quarantine size on low memory systems

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-693.1.1.vz7.37.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-693.1.1.vz7.37.4
------>
commit adcb15484ab1a2cf8e49fcf778bf42af2c423687
Author: Alexander Potapenko <glider at google.com>
Date:   Fri Sep 15 17:27:28 2017 +0300

    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.
    
    [akpm at linux-foundation.org: cleanup: use WARN_ONCE return value]
    Link: http://lkml.kernel.org/r/1470063563-96266-1-git-send-email-glider@google.com
    Fixes: 55834c59098d ("mm: kasan: initial memory quarantine implementation")
    Signed-off-by: Alexander Potapenko <glider at google.com>
    Reported-by: Dmitry Vyukov <dvyukov at google.com>
    Cc: Andrey Ryabinin <aryabinin at virtuozzo.com>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    
    https://jira.sw.ru/browse/PSBM-69081
    (cherry picked from commit c3cee372282cb6bcdf19ac1457581d5dd5ecb554)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/kasan/quarantine.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index 7fd121d..b6728a3 100644
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -198,7 +198,7 @@ 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;
@@ -216,7 +216,12 @@ 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 (WARN_ONCE(new_quarantine_size < percpu_quarantines,
+		"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;