[PATCH 4.14 060/496] ptr_ring: prevent integer overflow when calculating size

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jason Wang <jasowang@xxxxxxxxxx>

[ Upstream commit 54e02162d4454a99227f520948bf4494c3d972d0 ]

Switch to use dividing to prevent integer overflow when size is too
big to calculate allocation size properly.

Reported-by: Eric Biggers <ebiggers3@xxxxxxxxx>
Fixes: 6e6e41c31122 ("ptr_ring: fail early if queue occupies more than KMALLOC_MAX_SIZE")
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/ptr_ring.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -450,7 +450,7 @@ static inline int ptr_ring_consume_batch
  */
 static inline void **__ptr_ring_init_queue_alloc(unsigned int size, gfp_t gfp)
 {
-	if (size * sizeof(void *) > KMALLOC_MAX_SIZE)
+	if (size > KMALLOC_MAX_SIZE / sizeof(void *))
 		return NULL;
 	return kvmalloc_array(size, sizeof(void *), gfp | __GFP_ZERO);
 }