Re: [PATCH net v3] sctp: fix dst refcnt leak in sctp_v4_get_dst

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

On Mon, Feb 05, 2018 at 09:48:14PM +0200, Tommi Rantala wrote:
> Fix dst reference count leak in sctp_v4_get_dst() introduced in commit
> 410f03831 ("sctp: add routing output fallback"):
> 
> When walking the address_list, successive ip_route_output_key() calls
> may return the same rt->dst with the reference incremented on each call.
> 
> The code would not decrement the dst refcount when the dst pointer was
> identical from the previous iteration, causing the dst refcnt leak.
> 
> Testcase:
>   ip netns add TEST
>   ip netns exec TEST ip link set lo up
>   ip link add dummy0 type dummy
>   ip link add dummy1 type dummy
>   ip link add dummy2 type dummy
>   ip link set dev dummy0 netns TEST
>   ip link set dev dummy1 netns TEST
>   ip link set dev dummy2 netns TEST
>   ip netns exec TEST ip addr add 192.168.1.1/24 dev dummy0
>   ip netns exec TEST ip link set dummy0 up
>   ip netns exec TEST ip addr add 192.168.1.2/24 dev dummy1
>   ip netns exec TEST ip link set dummy1 up
>   ip netns exec TEST ip addr add 192.168.1.3/24 dev dummy2
>   ip netns exec TEST ip link set dummy2 up
>   ip netns exec TEST sctp_test -H 192.168.1.2 -P 20002 -h 192.168.1.1 -p 20000 -s -B 192.168.1.3
>   ip netns del TEST
> 
> In 4.4 and 4.9 kernels this results to:
>   [  354.179591] unregister_netdevice: waiting for lo to become free. Usage count = 1
>   [  364.419674] unregister_netdevice: waiting for lo to become free. Usage count = 1
>   [  374.663664] unregister_netdevice: waiting for lo to become free. Usage count = 1
>   [  384.903717] unregister_netdevice: waiting for lo to become free. Usage count = 1
>   [  395.143724] unregister_netdevice: waiting for lo to become free. Usage count = 1
>   [  405.383645] unregister_netdevice: waiting for lo to become free. Usage count = 1
>   ...
> 
> Fixes: 410f03831 ("sctp: add routing output fallback")
> Fixes: 0ca50d12f ("sctp: fix src address selection if using secondary addresses")
> Signed-off-by: Tommi Rantala <tommi.t.rantala@nokia.com>

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

Thanks

> ---
> 
> v2: unconditional dst_release() before breaking out of the loop:
>  - if dst == NULL, then dst_release() is no-op.
>  - if dst != &rt->dst, then drop reference to the first dst, we do not
>    need it after all.
>  - if dst == &rt->dst, then the refcnt was incremented twice for this
>    dst, so drop the second ref.
> 
>  net/sctp/protocol.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
> index ba28d270eb24..aba2381d3cf9 100644
> --- a/net/sctp/protocol.c
> +++ b/net/sctp/protocol.c
> @@ -509,22 +509,20 @@ static void sctp_v4_get_dst(struct sctp_transport *t, union sctp_addr *saddr,
>  		if (IS_ERR(rt))
>  			continue;
>  
> -		if (!dst)
> -			dst = &rt->dst;
> -
>  		/* Ensure the src address belongs to the output
>  		 * interface.
>  		 */
>  		odev = __ip_dev_find(sock_net(sk), laddr->a.v4.sin_addr.s_addr,
>  				     false);
>  		if (!odev || odev->ifindex != fl4->flowi4_oif) {
> -			if (&rt->dst != dst)
> +			if (!dst)
> +				dst = &rt->dst;
> +			else
>  				dst_release(&rt->dst);
>  			continue;
>  		}
>  
> -		if (dst != &rt->dst)
> -			dst_release(dst);
> +		dst_release(dst);
>  		dst = &rt->dst;
>  		break;
>  	}
> -- 
> 2.15.1
>