Re: [dpdk-dev] [PATCH v2] net/tap: fix potential buffer overrun

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 4/25/2019 6:17 PM, Herakliusz Lipiec wrote:
> When secondary to primary process synchronization occours
> there is no check for number of fds which could cause buffer overrun.
> 
> Bugzilla ID: 252
> Fixes: c9aa56edec8e ("net/tap: access primary process queues from secondary")
> Cc: rasland@mellanox.com
> Cc: stable@dpdk.org
> 
> Signed-off-by: Herakliusz Lipiec <herakliusz.lipiec@intel.com>
> ---
>  drivers/net/tap/rte_eth_tap.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
> index e9fda8cf6..4a2ef5ce7 100644
> --- a/drivers/net/tap/rte_eth_tap.c
> +++ b/drivers/net/tap/rte_eth_tap.c
> @@ -2111,6 +2111,10 @@ tap_mp_attach_queues(const char *port_name, struct rte_eth_dev *dev)
>  	TAP_LOG(DEBUG, "Received IPC reply for %s", reply_param->port_name);
>  
>  	/* Attach the queues from received file descriptors */
> +	if (reply_param->rxq_count + reply_param->txq_count != reply->num_fds) {
> +		TAP_LOG(ERR, "Unexpected number of fds received");
> +		return -1;
> +	}

Is there a way this can happen? If not I suggest remove the check.

>  	dev->data->nb_rx_queues = reply_param->rxq_count;
>  	dev->data->nb_tx_queues = reply_param->txq_count;
>  	fd_iterator = 0;
> @@ -2151,12 +2155,16 @@ tap_mp_sync_queues(const struct rte_mp_msg *request, const void *peer)
>  	/* Fill file descriptors for all queues */
>  	reply.num_fds = 0;
>  	reply_param->rxq_count = 0;
> +	if (dev->data->nb_rx_queues + dev->data->nb_tx_queues >
> +			RTE_MP_MAX_FD_NUM){
> +		TAP_LOG(ERR, "Number of rx/tx queues exceeds max number of fds");
> +		return -1;
> +	}

+1 for the check.
But what it does when return "-1", not send a message at all? If so would it be
better to send and error message back instead of waiting the receiver to timeout?

>  	for (queue = 0; queue < dev->data->nb_rx_queues; queue++) {
>  		reply.fds[reply.num_fds++] = process_private->rxq_fds[queue];
>  		reply_param->rxq_count++;
>  	}
>  	RTE_ASSERT(reply_param->rxq_count == dev->data->nb_rx_queues);
> -	RTE_ASSERT(reply_param->txq_count == dev->data->nb_tx_queues);
>  	RTE_ASSERT(reply.num_fds <= RTE_MP_MAX_FD_NUM);

Since there is dynamic check above for "RTE_MP_MAX_FD_NUM", we can remove this
assert I think.

>  
>  	reply_param->txq_count = 0;
> @@ -2164,7 +2172,8 @@ tap_mp_sync_queues(const struct rte_mp_msg *request, const void *peer)
>  		reply.fds[reply.num_fds++] = process_private->txq_fds[queue];
>  		reply_param->txq_count++;
>  	}
> -
> +	RTE_ASSERT(reply_param->txq_count == dev->data->nb_tx_queues);
> +	RTE_ASSERT(reply.num_fds <= RTE_MP_MAX_FD_NUM);

Same for this assert, we can remove it.
And as syntax, please keep the empty line before next block.

>  	/* Send reply */
>  	strlcpy(reply.name, request->name, sizeof(reply.name));
>  	strlcpy(reply_param->port_name, request_param->port_name,
>