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

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

On 4/29/2019 3:02 PM, Burakov, Anatoly wrote:
> 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.

Both sender and receiver are in the same driver, primary and secondary
application paths, there is no communication with external source,
and I don't see any code path that will cause this failure.

After above said, this is just an additional reasonable check and not in the
data path, so having this won't hurt, I don't object to have 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.

+1 to fix this issue but I assume it won't be for this release, so can get this
patch now and this part can be updated with mentioned patch.

> 
>>
>>>   	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,
>>>
>>
>>
> 
>