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

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 29-Apr-19 2:53 PM, Ferruh Yigit wrote:
> 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.

Normally no, but theoretically this can trigger a buffer overrun if not 
checked. After all, something could either fail on the other side, or 
someone could send a fake message :) This data is coming from an 
external source, so we need to sanity-check it.

> 
>>   	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?

There will be a different patch fixing this specific issue. Probably 
this patch would need to be rebased on top of that.

> 
>>   	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,
>>
> 
> 


-- 
Thanks,
Anatoly