Re: [PATCH] RDMA/nldev: add check for null return from call to nlmsg_put

[Leon Romanovsky]

On Thu, May 16, 2019 at 02:12:15PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>
> It is possible that nlmsg_put can return a null pointer, currently
> this will lead to a null pointer dereference when passing a null
> nlh pointer to nlmsg_end.  Fix this by adding a null pointer check.
>
> Addresses-Coverity: ("Dereference null return value")
> Fixes: cb7e0e130503 ("RDMA/core: Add interface to read device namespace sharing mode")
> Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> ---
>  drivers/infiniband/core/nldev.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/infiniband/core/nldev.c b/drivers/infiniband/core/nldev.c
> index 69188cbbd99b..4dc43b6c5a28 100644
> --- a/drivers/infiniband/core/nldev.c
> +++ b/drivers/infiniband/core/nldev.c
> @@ -1367,6 +1367,10 @@ static int nldev_sys_get_doit(struct sk_buff *skb, struct nlmsghdr *nlh,
>  			RDMA_NL_GET_TYPE(RDMA_NL_NLDEV,
>  					 RDMA_NLDEV_CMD_SYS_GET),
>  			0, 0);

It is impossible situation due to "0" in payload field above.

> +	if (!nlh) {
> +		nlmsg_free(msg);
> +		return -EMSGSIZE;
> +	}
>
>  	err = nla_put_u8(msg, RDMA_NLDEV_SYS_ATTR_NETNS_MODE,
>  			 (u8)ib_devices_shared_netns);
> --
> 2.20.1
>