RDMA/mlx5: Do not allow the user to write to the clock page

The intent of this VMA was to be read-only from user space, but the
VM_MAYWRITE masking was missed, so mprotect could make it writable.

Cc: stable@vger.kernel.org
Fixes: 5c99eaec ("IB/mlx5: Mmap the HCA's clock info to user-space")
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Haggai Eran <haggaie@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>

drivers/infiniband/hw/mlx5/main.c

@@ -2068,6 +2068,7 @@ static int mlx5_ib_mmap_clock_info_page(struct mlx5_ib_dev *dev,
 
 	if (vma->vm_flags & VM_WRITE)
 		return -EPERM;
+	vma->vm_flags &= ~VM_MAYWRITE;
 
 	if (!dev->mdev->clock_info_page)
 		return -EOPNOTSUPP;
@@ -2233,6 +2234,7 @@ static int mlx5_ib_mmap(struct ib_ucontext *ibcontext, struct vm_area_struct *vm
 
 		if (vma->vm_flags & VM_WRITE)
 			return -EPERM;
+		vma->vm_flags &= ~VM_MAYWRITE;
 
 		/* Don't expose to user-space information it shouldn't have */
 		if (PAGE_SIZE > 4096)