Re: [ovs-dev] [PATCH v2] net: openvswitch: fix possible memory leak in ovs_meter_cmd_set()

[Eelco Chaudron <echaudro@redhat.com>]

On 9 Feb 2023, at 11:58, Simon Horman wrote:

> On Thu, Feb 09, 2023 at 05:32:40PM +0800, Hangyu Hua wrote:
>> old_meter needs to be free after it is detached regardless of whether
>> the new meter is successfully attached.
>>
>> Fixes: c7c4c44c9a95 ("net: openvswitch: expand the meters supported number")
>> Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
>> ---
>>
>> v2: use goto label and free old_meter outside of ovs lock.
>>
>>  net/openvswitch/meter.c | 12 +++++++++---
>>  1 file changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/openvswitch/meter.c b/net/openvswitch/meter.c
>> index 6e38f68f88c2..9b680f0894f1 100644
>> --- a/net/openvswitch/meter.c
>> +++ b/net/openvswitch/meter.c
>> @@ -417,6 +417,7 @@ static int ovs_meter_cmd_set(struct sk_buff *skb, struct genl_info *info)
>>  	int err;
>>  	u32 meter_id;
>>  	bool failed;
>> +	bool locked = true;
>>
>>  	if (!a[OVS_METER_ATTR_ID])
>>  		return -EINVAL;
>> @@ -448,11 +449,13 @@ static int ovs_meter_cmd_set(struct sk_buff *skb, struct genl_info *info)
>>  		goto exit_unlock;
>>
>>  	err = attach_meter(meter_tbl, meter);
>> -	if (err)
>> -		goto exit_unlock;
>>
>>  	ovs_unlock();
>>
>> +	if (err) {
>> +		locked = false;
>> +		goto exit_free_old_meter;
>> +	}
>>  	/* Build response with the meter_id and stats from
>>  	 * the old meter, if any.
>>  	 */
>> @@ -472,8 +475,11 @@ static int ovs_meter_cmd_set(struct sk_buff *skb, struct genl_info *info)
>>  	genlmsg_end(reply, ovs_reply_header);
>>  	return genlmsg_reply(reply, info);
>>
>> +exit_free_old_meter:
>> +	ovs_meter_free(old_meter);
>>  exit_unlock:
>> -	ovs_unlock();
>> +	if (locked)
>> +		ovs_unlock();
>
> I see where you are going here, but is the complexity of the
> locked variable worth the benefit of freeing old_meter outside
> the lock?

Looking at the error path, I would agree with Simon, and just add an “exit_free_old_meter” label as suggested in v1 and keep the lock in place to make the error path more straightforward.

//Eelco

>>  	nlmsg_free(reply);
>>  exit_free_meter:
>>  	kfree(meter);
>> -- 
>> 2.34.1
>>
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