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

["Wiles, Keith" <keith.wiles@intel.com>]

> On Apr 25, 2019, at 10:17 AM, Lipiec, Herakliusz <herakliusz.lipiec@intel.com> 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;
> +	}

This check is reasonable, but why is this being done on the receive side and not checked on the send side. There may need to be a check for num_fds being zero or greater than 8 as that is the limit to the number of FDs that can be handle by the IPC.

In a different thread for Bug-258 we need to return an indicator that the receive side detected an error by returning 0 for num_fds and I have patch for that one.
https://bugs.dpdk.org/show_bug.cgi?id=258

I would have expected the sender to make sure they match and then this test is not needed, but a test for num_fds being zero or > 8 is needed if you want to detect the failure here or not if you do not care as long as nb_[r/t]x_queues is zero too.

> 	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;
> +	}
> 	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);
> 
> 	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);
> 	/* Send reply */
> 	strlcpy(reply.name, request->name, sizeof(reply.name));
> 	strlcpy(reply_param->port_name, request_param->port_name,
> -- 
> 2.17.2
> 

Regards,
Keith