Re: [PATCH for-rc] IB/mlx4: Fix leak in id_map_find_del

["Håkon Bugge" <haakon.bugge@oracle.com>]

> On 20 Jan 2020, at 17:27, Leon Romanovsky <leon@kernel.org> wrote:
> 
> On Mon, Jan 20, 2020 at 04:49:56PM +0100, Håkon Bugge wrote:
>> 
>> 
>>> On 20 Jan 2020, at 16:06, Leon Romanovsky <leon@kernel.org> wrote:
>>> 
>>> On Fri, Jan 17, 2020 at 02:56:22PM +0100, Håkon Bugge wrote:
>>>> Using CX-3 virtual functions, either from a bare-metal machine or
>>>> pass-through from a VM, MAD packets are proxied through the PF driver.
>>>> 
>>>> Since the VF drivers have separate name spaces for MAD Transaction Ids
>>>> (TIDs), the PF driver has to re-map the TIDs and keep the book keeping
>>>> in a cache.
>>>> 
>>>> Following the RDMA Connection Manager (CM) protocol, it is clear when
>>>> an entry has to evicted from the cache. When a DREP is sent from
>>>> mlx4_ib_multiplex_cm_handler(), id_map_find_del() is called. Similar
>>>> when a REJ is received by the mlx4_ib_demux_cm_handler(),
>>>> id_map_find_del() is called.
>>>> 
>>>> This function wipes out the TID in use from the IDR or XArray and
>>>> removes the id_map_entry from the table.
>>>> 
>>>> In short, it does everything except the topping of the cake, which is
>>>> to remove the entry from the list and free it. In other words, for the
>>>> DREP and REJ cases enumerated above, both will leak one id_map_entry.
>>>> 
>>>> Signed-off-by: Håkon Bugge <haakon.bugge@oracle.com>
>>>> ---
>>>> drivers/infiniband/hw/mlx4/cm.c | 7 ++++++-
>>>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>>> 
>>>> diff --git a/drivers/infiniband/hw/mlx4/cm.c b/drivers/infiniband/hw/mlx4/cm.c
>>>> index ecd6cadd529a..1df6d3ccfc62 100644
>>>> --- a/drivers/infiniband/hw/mlx4/cm.c
>>>> +++ b/drivers/infiniband/hw/mlx4/cm.c
>>>> @@ -197,8 +197,13 @@ static void id_map_find_del(struct ib_device *ibdev, int pv_cm_id)
>>>> 	if (!ent)
>>>> 		goto out;
>>>> 	found_ent = id_map_find_by_sl_id(ibdev, ent->slave_id, ent->sl_cm_id);
>>>> -	if (found_ent && found_ent == ent)
>>>> +	if (found_ent && found_ent == ent) {
>>>> 		rb_erase(&found_ent->node, sl_id_map);
>>>> +		if (!ent->scheduled_delete) {
>>> 
>>> Why do we need to check scheduled_delete?
>> 
>> 1. Node receives a DREQ and mlx4_ib_demux_cm_handler() is called, which again calls schedule_delayed(), which sets scheduled_delete.
>> 
>> 2. DREQ is proxied over to the VM, which replies with a DREP.
>> 
>> 3. The DREP is proxied over to the PF driver, mlx4_ib_multiplex_cm_handler() is called, id_map_find_del() is called. If it is freed now (without checking scheduled_delete), it will be a double free when the delayed work kicks in.
> 
> It will be the case if we don't cancel delayed work inside
> id_map_find_del(), but it raises other question. Why do we need two
> identical delete functions?

Almost identical. It's a question about being evolutionary vs. revolutionary, when fixing a leak. My preference would be to fix the leak as simple as possible, without changing any logic.

> Can we convert id_map_find_del() callers
> to use id_map_ent_timeout() instead?

I did the opposite, and I will send it out as a v2 after testing. But, I didn't like it. Fewer lines, yes, but more complexity.


Thxs, Håkon

> 
> Thanks
> 
>> 
>> But this documents that the commit message is not accurate, it is only the REJ case that has a leak.
>> 
>>> Isn't this to mark call to timeout cleanup (id_map_ent_timeout), which
>>> can't race with id_map_find_del()? They both hold the same spinlock.
>> 
>> No race, but it can be set as per the above.
>> 
>> If you agree, I will send a v2 with corrected commit message.
>> 
>> 
>> Thxs, Håkon
>> 
>> 
>>> 
>>> Thanks
>>> 
>>>> +			list_del(&ent->list);
>>>> +			kfree(ent);
>>>> +		}
>>>> +	}
>>>> out:
>>>> 	spin_unlock(&sriov->id_map_lock);
>>>> }
>>>> --
>>>> 2.20.1