Re: [dpdk-dev] [PATCH 2/2] net/bonding: avoid the next active slave going out of bound

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

On 2/11/2019 10:25 AM, Parthasarathy, JananeeX M wrote:
> Hi
> 
>> -----Original Message-----
>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Chas Williams
>> Sent: Saturday, February 09, 2019 6:47 PM
>> To: Hyong Youb Kim <hyonkim@cisco.com>; Yigit, Ferruh
>> <ferruh.yigit@intel.com>; Doherty, Declan <declan.doherty@intel.com>; Chas
>> Williams <chas3@att.com>
>> Cc: dev@dpdk.org; stable@dpdk.org
>> Subject: Re: [dpdk-dev] [PATCH 2/2] net/bonding: avoid the next active slave
>> going out of bound
>>
>>
>>
>> On 1/10/19 5:22 AM, Hyong Youb Kim wrote:
>>> For bonding modes like broadcast that use bond_ethdev_rx_burst(), it
>>> is fairly easy to produce a crash simply by bringing a slave port's
>>> link down. When slave links go down, the driver on one thread reduces
>>> active_slave_count via the LSC callback and deactivate_slave(). At the
>>> same time, bond_ethdev_rx_burst() running on a forwarding thread may
>>> increment active_slave (next active slave) beyond active_slave_count.
>>> Here is a typical sequence of events.
>>>
>>> At time 0:
>>> active_slave_count = 3
>>> active_slave = 2
>>>
>>> At time 1:
>>> A slave link goes down.
>>> Thread 0 (main) reduces active_slave_count to 2.
>>>
>>> At time 2:
>>> Thread 1 (forwarding) executes bond_ethdev_rx_burst().
>>> - Reads active_slave_count = 2.
>>> - Increments active_slave at the end to 3.
>>>
>>>  From this point on, everytime bond_ethdev_rx_burst() runs,
>>> active_slave increments by one, eventually going well out of bound of
>>> the active_slaves array and causing a crash.
>>>
>>> Make the rx burst function to first check that active_slave is within
>>> bound. If not, reset it to 0 to avoid out-of-range array access.
>>>
>>> Fixes: e1110e977648 ("net/bonding: fix Rx slave fairness")
>>> Cc: stable@dpdk.org
>>>
>>> Signed-off-by: Hyong Youb Kim <hyonkim@cisco.com>
>>
>> Acked-by: Chas Williams <chas3@att.com>
>>
>>> ---
>>>   drivers/net/bonding/rte_eth_bond_pmd.c | 14 ++++++++++++++
>>>   1 file changed, 14 insertions(+)
>>>
>>> diff --git a/drivers/net/bonding/rte_eth_bond_pmd.c
>>> b/drivers/net/bonding/rte_eth_bond_pmd.c
>>> index daf2440cd..bc2405e54 100644
>>> --- a/drivers/net/bonding/rte_eth_bond_pmd.c
>>> +++ b/drivers/net/bonding/rte_eth_bond_pmd.c
>>> @@ -68,6 +68,15 @@ bond_ethdev_rx_burst(void *queue, struct rte_mbuf
>> **bufs, uint16_t nb_pkts)
>>>   	internals = bd_rx_q->dev_private;
>>>   	slave_count = internals->active_slave_count;
>>>   	active_slave = internals->active_slave;
>>> +	/*
>>> +	 * Reset the active slave index, in case active_slave goes out
>>> +	 * of bound.  It can hapen when slave links go down, and
>>> +	 * another thread (LSC callback) shrinks the slave count.
>>> +	 */
>>> +	if (active_slave >= slave_count) {
>>> +		internals->active_slave = 0;
>>> +		active_slave = 0;
>>> +	}
> 
> Instead of introducing new conditions again at the top of functions, it would be better to check greater than, equal to >= instead of the equal to  in below condition.
> if (++internals->active_slave == slave_count)
>                 internals->active_slave = 0;
> 
> Thereby we can reduce the multiple if conditions and still ensure internals->active_slave points to correct index always.
> 
>>>
>>>   	for (i = 0; i < slave_count && nb_pkts; i++) {
>>>   		uint16_t num_rx_slave;
>>> @@ -273,6 +282,11 @@ bond_ethdev_rx_burst_8023ad_fast_queue(void
>> *queue, struct rte_mbuf **bufs,
>>>   	active_slave = internals->active_slave;
>>>   	memcpy(slaves, internals->active_slaves,
>>>   			sizeof(internals->active_slaves[0]) * slave_count);
>>> +	/* active_slave may go out of bound. See bond_ethdev_rx_burst() */
>>> +	if (active_slave >= slave_count) {
>>> +		internals->active_slave = 0;
>>> +		active_slave = 0;
>>> +	}
> 
> Same as above comment would be better.
>>>
>>>   	for (i = 0; i < slave_count && nb_pkts; i++) {
>>>   		uint16_t num_rx_slave;
>>>
> 
> It would be better to check the internals->active_slave during deactivate_slave() as well in rte_eth_bond_api.c.
> Since slave counts would be decremented during de-activation and resetting here appropriately would be better.
> 
> Regards
> M.P.Jananee


I don't see this comment on the patchwork, can you double check if your comment
hit the mailing list?