[PATCH][next] vhost: Use flex_array_size() helper in copy_from_user()

["Gustavo A. R. Silva" <gustavoars@kernel.org>]

Make use of the flex_array_size() helper to calculate the size of a
flexible array member within an enclosing structure.

This helper offers defense-in-depth against potential integer
overflows, while at the same time makes it explicitly clear that
we are dealing with a flexible array member.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/vhost/vhost.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 74d135ee7e26..1a22a254abe4 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1405,7 +1405,7 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
 
 	memcpy(newmem, &mem, size);
 	if (copy_from_user(newmem->regions, m->regions,
-			   mem.nregions * sizeof *m->regions)) {
+			   flex_array_size(newmem, regions, mem.nregions))) {
 		kvfree(newmem);
 		return -EFAULT;
 	}
-- 
2.27.0