Re: [Qemu-devel] [PATCH 1/5] rdma: check that num_sge does not exceed MAX_SGE

[Yuval Shaia <yuval.shaia@oracle.com>]

On Tue, Dec 11, 2018 at 06:56:38PM +0530, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> rdma back-end has scatter/gather array ibv_sge[MAX_SGE=4] set
> to have 4 elements. A guest could send a 'PvrdmaSqWqe' ring element
> with 'num_sge' set to > MAX_SGE, which may lead to OOB access issue.
> Add check to avoid it.
> 
> Reported-by: Saar Amar <saaramar5@gmail.com>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/rdma/rdma_backend.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/rdma/rdma_backend.c b/hw/rdma/rdma_backend.c
> index d7a4bbd91f..0b3b98a94c 100644
> --- a/hw/rdma/rdma_backend.c
> +++ b/hw/rdma/rdma_backend.c
> @@ -311,8 +311,8 @@ void rdma_backend_post_send(RdmaBackendDev *backend_dev,
>      }
>  
>      pr_dbg("num_sge=%d\n", num_sge);
> -    if (!num_sge) {
> -        pr_dbg("num_sge=0\n");
> +    if (!num_sge || num_sge > MAX_SGE) {
> +        pr_dbg("invalid num_sge=%d\n", num_sge);
>          comp_handler(IBV_WC_GENERAL_ERR, VENDOR_ERR_NO_SGE, ctx);

Please use VENDOR_ERR_INV_NUM_SGE

>          return;
>      }
> @@ -390,8 +390,8 @@ void rdma_backend_post_recv(RdmaBackendDev *backend_dev,
>      }
>  
>      pr_dbg("num_sge=%d\n", num_sge);
> -    if (!num_sge) {
> -        pr_dbg("num_sge=0\n");
> +    if (!num_sge || num_sge > MAX_SGE) {
> +        pr_dbg("invalid num_sge=%d\n", num_sge);
>          comp_handler(IBV_WC_GENERAL_ERR, VENDOR_ERR_NO_SGE, ctx);

Ditto.

And since VENDOR_ERR_NO_SGE is no loger used it can be delete.

>          return;
>      }
> -- 
> 2.19.2
>