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@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@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index 7fd121d13b88..b6728a33a4ac 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;