Re: [net] tipc: fix NULL pointer dereference in tipc_named_rcv

[Jon Maloy <jmaloy@redhat.com>]

On 10/9/20 12:12 AM, Hoang Huu Le wrote:
> Hi Jon,  Jakub,
>
> I tried with your comment. But looks like we got into circular locking and deadlock could happen like this:
>          CPU0                    CPU1
>          ----                    ----
>     lock(&n->lock#2);
>                                  lock(&tn->nametbl_lock);
>                                  lock(&n->lock#2);
>     lock(&tn->nametbl_lock);
>
>    *** DEADLOCK ***
>
> Regards,
> Hoang
Ok. So although your solution is not optimal, we know it is safe.
Again:
Acked-by: Jon Maloy <jmaloy@redhat.com>
>> -----Original Message-----
>> From: Jon Maloy <jmaloy@redhat.com>
>> Sent: Friday, October 9, 2020 1:01 AM
>> To: Jakub Kicinski <kuba@kernel.org>; Hoang Huu Le <hoang.h.le@dektech.com.au>
>> Cc: maloy@donjonn.com; ying.xue@windriver.com; tipc-discussion@lists.sourceforge.net; netdev@vger.kernel.org
>> Subject: Re: [net] tipc: fix NULL pointer dereference in tipc_named_rcv
>>
>>
>>
>> On 10/8/20 1:25 PM, Jakub Kicinski wrote:
>>> On Thu,  8 Oct 2020 14:31:56 +0700 Hoang Huu Le wrote:
>>>> diff --git a/net/tipc/name_distr.c b/net/tipc/name_distr.c
>>>> index 2f9c148f17e2..fe4edce459ad 100644
>>>> --- a/net/tipc/name_distr.c
>>>> +++ b/net/tipc/name_distr.c
>>>> @@ -327,8 +327,13 @@ static struct sk_buff *tipc_named_dequeue(struct sk_buff_head *namedq,
>>>>    	struct tipc_msg *hdr;
>>>>    	u16 seqno;
>>>>
>>>> +	spin_lock_bh(&namedq->lock);
>>>>    	skb_queue_walk_safe(namedq, skb, tmp) {
>>>> -		skb_linearize(skb);
>>>> +		if (unlikely(skb_linearize(skb))) {
>>>> +			__skb_unlink(skb, namedq);
>>>> +			kfree_skb(skb);
>>>> +			continue;
>>>> +		}
>>>>    		hdr = buf_msg(skb);
>>>>    		seqno = msg_named_seqno(hdr);
>>>>    		if (msg_is_last_bulk(hdr)) {
>>>> @@ -338,12 +343,14 @@ static struct sk_buff *tipc_named_dequeue(struct sk_buff_head *namedq,
>>>>
>>>>    		if (msg_is_bulk(hdr) || msg_is_legacy(hdr)) {
>>>>    			__skb_unlink(skb, namedq);
>>>> +			spin_unlock_bh(&namedq->lock);
>>>>    			return skb;
>>>>    		}
>>>>
>>>>    		if (*open && (*rcv_nxt == seqno)) {
>>>>    			(*rcv_nxt)++;
>>>>    			__skb_unlink(skb, namedq);
>>>> +			spin_unlock_bh(&namedq->lock);
>>>>    			return skb;
>>>>    		}
>>>>
>>>> @@ -353,6 +360,7 @@ static struct sk_buff *tipc_named_dequeue(struct sk_buff_head *namedq,
>>>>    			continue;
>>>>    		}
>>>>    	}
>>>> +	spin_unlock_bh(&namedq->lock);
>>>>    	return NULL;
>>>>    }
>>>>
>>>> diff --git a/net/tipc/node.c b/net/tipc/node.c
>>>> index cf4b239fc569..d269ebe382e1 100644
>>>> --- a/net/tipc/node.c
>>>> +++ b/net/tipc/node.c
>>>> @@ -1496,7 +1496,7 @@ static void node_lost_contact(struct tipc_node *n,
>>>>
>>>>    	/* Clean up broadcast state */
>>>>    	tipc_bcast_remove_peer(n->net, n->bc_entry.link);
>>>> -	__skb_queue_purge(&n->bc_entry.namedq);
>>>> +	skb_queue_purge(&n->bc_entry.namedq);
>>> Patch looks fine, but I'm not sure why not hold
>>> spin_unlock_bh(&tn->nametbl_lock) here instead?
>>>
>>> Seems like node_lost_contact() should be relatively rare,
>>> so adding another lock to tipc_named_dequeue() is not the
>>> right trade off.
>> Actually, I agree with previous speaker here. We already have the
>> nametbl_lock when tipc_named_dequeue() is called, and the same lock is
>> accessible from no.c where node_lost_contact() is executed. The patch
>> and the code becomes simpler.
>> I suggest you post a v2 of this one.
>>
>> ///jon
>>
>>>>    	/* Abort any ongoing link failover */
>>>>    	for (i = 0; i < MAX_BEARERS; i++) {