Re: [PATCH for-next] RDMA/core: Fix storing node_desc

[Jason Gunthorpe <jgg@ziepe.ca>]

On Mon, Dec 23, 2019 at 11:39:43AM +0200, Kamal Heib wrote:
> When writing to node_desc sysfs using echo a new line symbol will be
> stored at the end of the string, avoid that by dropping the new line

Why do we want to do this? AFAIK technically new line is valid in a
node description.

> symbol and also make sure to return -EINVAL when the supplied string is
> bigger then IB_DEVICE_NODE_DESC_MAX.

This makes sense though

> diff --git a/drivers/infiniband/core/sysfs.c b/drivers/infiniband/core/sysfs.c
> index 087682e6969e..2de5f6710c0b 100644
> +++ b/drivers/infiniband/core/sysfs.c
> @@ -1263,12 +1263,21 @@ static ssize_t node_desc_store(struct device *device,
>  {
>  	struct ib_device *dev = rdma_device_to_ibdev(device);
>  	struct ib_device_modify desc = {};
> +	size_t len;
>  	int ret;
>  
>  	if (!dev->ops.modify_device)
>  		return -EOPNOTSUPP;
>  
> -	memcpy(desc.node_desc, buf, min_t(int, count, IB_DEVICE_NODE_DESC_MAX));

> +	if (count > IB_DEVICE_NODE_DESC_MAX)
> +		return -EINVAL;
> +
> +	len = strlen(buf);

Why strlen? The buf is count bytes long.

> +	if (buf[len - 1] == '\n')
> +		len--;

And if it is zero bytes this buffer underflows

> +	strncpy(desc.node_desc, buf, len);

What was the point of switching away from memcpy?

> +	desc.node_desc[len] = 0;
>  	ret = ib_modify_device(dev, IB_DEVICE_MODIFY_NODE_DESC, &desc);
>  	if (ret)
>  		return ret;

Jason