[PATCH v2] dma-buf/heaps: system_heap: Avoid DoS by limiting single allocations to half of all memory

[Jaewon Kim <jaewon31.kim@samsung.com>]

Normal free:212600kB min:7664kB low:57100kB high:106536kB
  reserved_highatomic:4096KB active_anon:276kB inactive_anon:180kB
  active_file:1200kB inactive_file:0kB unevictable:2932kB
  writepending:0kB present:4109312kB managed:3689488kB mlocked:2932kB
  pagetables:13600kB bounce:0kB free_pcp:0kB local_pcp:0kB
  free_cma:200844kB
Out of memory and no killable processes...
Kernel panic - not syncing: System is deadlocked on memory

An OoM panic was reported, there were only native processes which are
non-killable as OOM_SCORE_ADJ_MIN.

After looking into the dump, I've found the dma-buf system heap was
trying to allocate a huge size. It seems to be a signed negative value.

dma_heap_ioctl_allocate(inline)
    |  heap_allocation = 0xFFFFFFC02247BD38 -> (
    |    len = 0xFFFFFFFFE7225100,

Actually the old ion system heap had policy which does not allow that
huge size with commit c9e8440eca61 ("staging: ion: Fix overflow and list
bugs in system heap"). We need this change again. Single allocation
should not be bigger than half of all memory.

Signed-off-by: Jaewon Kim <jaewon31.kim@samsung.com>
Acked-by: John Stultz <jstultz@google.com>
Reviewed-by: T.J. Mercier <tjmercier@google.com>
---
 drivers/dma-buf/heaps/system_heap.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
index e8bd10e60998..4c1ef2ecfb0f 100644
--- a/drivers/dma-buf/heaps/system_heap.c
+++ b/drivers/dma-buf/heaps/system_heap.c
@@ -351,6 +351,9 @@ static struct dma_buf *system_heap_allocate(struct dma_heap *heap,
 	struct page *page, *tmp_page;
 	int i, ret = -ENOMEM;
 
+	if (len / PAGE_SIZE > totalram_pages() / 2)
+		return ERR_PTR(-ENOMEM);
+
 	buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
 	if (!buffer)
 		return ERR_PTR(-ENOMEM);
-- 
2.17.1