APPLIED: ACK: [OEM-5.6][SRU][PATCHv2 1/1] l2tp: remove skb_dst_set() from l2tp_xmit_skb()

[Tim Gardner]

Applied to focal:linux-oem-5.6/oem-5.6-next. Thanks.

-rtg

On 3/31/21 8:03 AM, Tim Gardner wrote:
> Acked-by: Tim Gardner <tim.gardner at canonical.com>
> 
> On 3/25/21 1:39 AM, Po-Hsu Lin wrote:
>> From: Xin Long <lucien.xin at gmail.com>
>>
>> BugLink: https://bugs.launchpad.net/bugs/1919277
>>
>> In the tx path of l2tp, l2tp_xmit_skb() calls skb_dst_set() to set
>> skb's dst. However, it will eventually call inet6_csk_xmit() or
>> ip_queue_xmit() where skb's dst will be overwritten by:
>>
>>     skb_dst_set_noref(skb, dst);
>>
>> without releasing the old dst in skb. Then it causes dst/dev refcnt leak:
>>
>>    unregister_netdevice: waiting for eth0 to become free. Usage count = 1
>>
>> This can be reproduced by simply running:
>>
>>    # modprobe l2tp_eth && modprobe l2tp_ip
>>    # sh ./tools/testing/selftests/net/l2tp.sh
>>
>> So before going to inet6_csk_xmit() or ip_queue_xmit(), skb's dst
>> should be dropped. This patch is to fix it by removing skb_dst_set()
>> from l2tp_xmit_skb() and moving skb_dst_drop() into l2tp_xmit_core().
>>
>> Fixes: 3557baabf280 ("[L2TP]: PPP over L2TP driver core")
>> Reported-by: Hangbin Liu <liuhangbin at gmail.com>
>> Signed-off-by: Xin Long <lucien.xin at gmail.com>
>> Acked-by: James Chapman <jchapman at katalix.com>
>> Tested-by: James Chapman <jchapman at katalix.com>
>> Signed-off-by: David S. Miller <davem at davemloft.net>
>> (cherry picked from commit 27d53323664c549b5bb2dfaaf6f7ad6e0376a64e)
>> Signed-off-by: Po-Hsu Lin <po-hsu.lin at canonical.com>
>> ---
>>   net/l2tp/l2tp_core.c | 5 +----
>>   1 file changed, 1 insertion(+), 4 deletions(-)
>>
>> diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
>> index 6d7ef78..6434d17 100644
>> --- a/net/l2tp/l2tp_core.c
>> +++ b/net/l2tp/l2tp_core.c
>> @@ -1028,6 +1028,7 @@ static void l2tp_xmit_core(struct l2tp_session 
>> *session, struct sk_buff *skb,
>>       /* Queue the packet to IP for output */
>>       skb->ignore_df = 1;
>> +    skb_dst_drop(skb);
>>   #if IS_ENABLED(CONFIG_IPV6)
>>       if (l2tp_sk_is_v6(tunnel->sock))
>>           error = inet6_csk_xmit(tunnel->sock, skb, NULL);
>> @@ -1099,10 +1100,6 @@ int l2tp_xmit_skb(struct l2tp_session *session, 
>> struct sk_buff *skb, int hdr_len
>>           goto out_unlock;
>>       }
>> -    /* Get routing info from the tunnel socket */
>> -    skb_dst_drop(skb);
>> -    skb_dst_set(skb, sk_dst_check(sk, 0));
>> -
>>       inet = inet_sk(sk);
>>       fl = &inet->cork.fl;
>>       switch (tunnel->encap) {
>>
> 

-- 
-----------
Tim Gardner
Canonical, Inc