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Date: Fri, 20 Apr 2018 13:46:30 +0800
From: Yanjun Zhu <yanjun.zhu@...cle.com>
To: Doug Ledford <dledford@...hat.com>, monis@...lanox.com,
jgg@...pe.ca, linux-rdma@...r.kernel.org
Cc: netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/1] IB/rxe: avoid double kfree_skb
On 2018/4/20 10:19, Doug Ledford wrote:
> On Thu, 2018-04-19 at 10:01 -0400, Zhu Yanjun wrote:
>> When skb is dropped by iptables rules, the skb is freed at the same time
>> -EPERM is returned. So in softroce, it is not necessary to free skb again.
>> Or else, crash will occur.
>>
>> The steps to reproduce:
>>
>> server client
>> --------- ---------
>> |1.1.1.1|<----rxe-channel--->|1.1.1.2|
>> --------- ---------
>>
>> On server: rping -s -a 1.1.1.1 -v -C 10000 -S 512
>> On client: rping -c -a 1.1.1.1 -v -C 10000 -S 512
>>
>> The kernel configs CONFIG_DEBUG_KMEMLEAK and
>> CONFIG_DEBUG_OBJECTS are enabled on both server and client.
>>
>> When rping runs, run the following command in server:
>>
>> iptables -I OUTPUT -p udp --dport 4791 -j DROP
>>
>> Without this patch, crash will occur.
>>
>> CC: Srinivas Eeda <srinivas.eeda@...cle.com>
>> CC: Junxiao Bi <junxiao.bi@...cle.com>
>> Signed-off-by: Zhu Yanjun <yanjun.zhu@...cle.com>
>> Reviewed-by: Yuval Shaia <yuval.shaia@...cle.com>
> I have no reason to doubt your analysis, but if there are a bunch of
> error paths for net_xmit and they all return with your skb still being
> valid and holding a reference, and then one oddball that returns with
> your skb already gone, that just sounds like a mistake waiting to happen
> (not to mention a bajillion special cases sprinkled everywhere to deal
> with this apparent inconsistency).
>
> Can we get a netdev@ confirmation on this being the right solution?
Yes. I agree with you.
After iptables rule "iptables -I OUTPUT -p udp --dport 4791 -j DROP",
the skb is freed in this function
/* Returns 1 if okfn() needs to be executed by the caller,
* -EPERM for NF_DROP, 0 otherwise. Caller must hold rcu_read_lock. */
int nf_hook_slow(struct sk_buff *skb, struct nf_hook_state *state,
const struct nf_hook_entries *e, unsigned int s)
{
unsigned int verdict;
int ret;
for (; s < e->num_hook_entries; s++) {
verdict = nf_hook_entry_hookfn(&e->hooks[s], skb, state);
switch (verdict & NF_VERDICT_MASK) {
case NF_ACCEPT:
break;
case NF_DROP:
kfree_skb(skb); <----here, skb is freed
ret = NF_DROP_GETERR(verdict);
if (ret == 0)
ret = -EPERM;
return ret;
case NF_QUEUE:
ret = nf_queue(skb, state, e, s, verdict);
if (ret == 1)
continue;
return ret;
default:
/* Implicit handling for NF_STOLEN, as well as
any other
* non conventional verdicts.
*/
return 0;
}
}
return 1;
}
EXPORT_SYMBOL(nf_hook_slow);
If I am wrong, please correct me.
And my test environment is still there, any solution can be verified in it.
Zhu Yanjun
>
>> ---
>> drivers/infiniband/sw/rxe/rxe_net.c | 3 +++
>> drivers/infiniband/sw/rxe/rxe_req.c | 5 +++--
>> drivers/infiniband/sw/rxe/rxe_resp.c | 9 ++++++---
>> 3 files changed, 12 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/infiniband/sw/rxe/rxe_net.c b/drivers/infiniband/sw/rxe/rxe_net.c
>> index 9da6e37..2094434 100644
>> --- a/drivers/infiniband/sw/rxe/rxe_net.c
>> +++ b/drivers/infiniband/sw/rxe/rxe_net.c
>> @@ -511,6 +511,9 @@ int rxe_send(struct rxe_pkt_info *pkt, struct sk_buff *skb)
>>
>> if (unlikely(net_xmit_eval(err))) {
>> pr_debug("error sending packet: %d\n", err);
>> + /* -EPERM means the skb is dropped and freed. */
>> + if (err == -EPERM)
>> + return -EPERM;
>> return -EAGAIN;
>> }
>>
>> diff --git a/drivers/infiniband/sw/rxe/rxe_req.c b/drivers/infiniband/sw/rxe/rxe_req.c
>> index 7bdaf71..9d2efec 100644
>> --- a/drivers/infiniband/sw/rxe/rxe_req.c
>> +++ b/drivers/infiniband/sw/rxe/rxe_req.c
>> @@ -727,8 +727,9 @@ int rxe_requester(void *arg)
>>
>> rollback_state(wqe, qp, &rollback_wqe, rollback_psn);
>>
>> - if (ret == -EAGAIN) {
>> - kfree_skb(skb);
>> + if ((ret == -EAGAIN) || (ret == -EPERM)) {
>> + if (ret == -EAGAIN)
>> + kfree_skb(skb);
>> rxe_run_task(&qp->req.task, 1);
>> goto exit;
>> }
>> diff --git a/drivers/infiniband/sw/rxe/rxe_resp.c b/drivers/infiniband/sw/rxe/rxe_resp.c
>> index a65c996..6bdf9b2 100644
>> --- a/drivers/infiniband/sw/rxe/rxe_resp.c
>> +++ b/drivers/infiniband/sw/rxe/rxe_resp.c
>> @@ -742,7 +742,8 @@ static enum resp_states read_reply(struct rxe_qp *qp,
>> err = rxe_xmit_packet(rxe, qp, &ack_pkt, skb);
>> if (err) {
>> pr_err("Failed sending RDMA reply.\n");
>> - kfree_skb(skb);
>> + if (err != -EPERM)
>> + kfree_skb(skb);
>> return RESPST_ERR_RNR;
>> }
>>
>> @@ -956,7 +957,8 @@ static int send_ack(struct rxe_qp *qp, struct rxe_pkt_info *pkt,
>> err = rxe_xmit_packet(rxe, qp, &ack_pkt, skb);
>> if (err) {
>> pr_err_ratelimited("Failed sending ack\n");
>> - kfree_skb(skb);
>> + if (err != -EPERM)
>> + kfree_skb(skb);
>> }
>>
>> err1:
>> @@ -1141,7 +1143,8 @@ static enum resp_states duplicate_request(struct rxe_qp *qp,
>> if (rc) {
>> pr_err("Failed resending result. This flow is not handled - skb ignored\n");
>> rxe_drop_ref(qp);
>> - kfree_skb(skb_copy);
>> + if (rc != -EPERM)
>> + kfree_skb(skb_copy);
>> rc = RESPST_CLEANUP;
>> goto out;
>> }
>> --
>> 2.7.4
>>
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