Re: [dpdk-stable] [PATCH] ethdev: avoid undefined behaviour on configuration copying

[Andrew Rybchenko <arybchenko@solarflare.com>]

On 11/19/19 3:24 PM, Ferruh Yigit wrote:
> On 11/19/2019 8:22 AM, Andrew Rybchenko wrote:
>> memcpy() source and destination areas must not overlap and equal
>> pointers is the case which is really met, so handle it.
> Agree providing same config as input can cause problem with current
> implementation, but it is the limitation of the memcpy, the API doesn't request
> this.
>
> We can fix as you suggested, in this case we should document this in API
> documentation I think,

Basically the patch solves it and there is nothing to document.
If pointers are equal there is nothing to do, no copying required.

> we can also solve this by updating the implementation to let this, using an
> interim buffer in the simplest measure, not sure which one is better.

I don't think that interim buffer is required, 'if' perfectly does the job.

> Any practical reason to prevent this other than 'memcpy' limitation?

Nothing except application should not play with dev->data,
but I'm not sure if it is the right place to forbid it.

Alternative solution is to fix bonding and return error if dev_conf is
equal to &dev->data->dev_conf since usecase is unclear and callers
should not use dev->data.

>> Fixes: 68b931bff287 ("ethdev: eliminate interim variable")
>> Cc: stable@dpdk.org
>>
>> Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
>> ---
>> slave_configure() in drivers/net/bonding calls rte_eth_dev_configure()
>> with &slave_eth_dev->data->dev_conf.
>>
>> Alternative solution is to fix bonding and return error if dev_conf is
>> equal to &dev->data->dev_conf since usecase is unclear and callers
>> should not use dev->data.
>>
>>  lib/librte_ethdev/rte_ethdev.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c
>> index 8f48e8d659..8d2ce31a81 100644
>> --- a/lib/librte_ethdev/rte_ethdev.c
>> +++ b/lib/librte_ethdev/rte_ethdev.c
>> @@ -1245,7 +1245,9 @@ rte_eth_dev_configure(uint16_t port_id, uint16_t nb_rx_q, uint16_t nb_tx_q,
>>  	 * Copy the dev_conf parameter into the dev structure.
>>  	 * rte_eth_dev_info_get() requires dev_conf, copy it before dev_info get
>>  	 */
>> -	memcpy(&dev->data->dev_conf, dev_conf, sizeof(dev->data->dev_conf));
>> +	if (dev_conf != &dev->data->dev_conf)
>> +		memcpy(&dev->data->dev_conf, dev_conf,
>> +		       sizeof(dev->data->dev_conf));
>>  
>>  	ret = rte_eth_dev_info_get(port_id, &dev_info);
>>  	if (ret != 0)
>>