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

[Tim Gardner]

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