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

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

[Tommi Rantala]

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>
---

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

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

[Marcelo Ricardo Leitner]

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
> 

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

[David Ahern]

On 2/5/18 12:48 PM, 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.
> 
...
>   ...
> 
> Fixes: 410f03831 ("sctp: add routing output fallback")
> Fixes: 0ca50d12f ("sctp: fix src address selection if using secondary addresses")

any syzbot references for this bug?

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

[Neil Horman]

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>
> ---
> 
> 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
> 
> 
Acked-by: Neil Horman <nhorman@tuxdriver.com>

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

[David Miller]

From: Tommi Rantala <tommi.t.rantala@nokia.com>
Date: Mon,  5 Feb 2018 21:48:14 +0200

> 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.
 ...
> 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>

Applied and queued up for -stable, thanks.

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

[Xin Long]

On Tue, Feb 6, 2018 at 7:20 AM, David Ahern <dsahern@gmail.com> wrote:
> On 2/5/18 12:48 PM, 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.
>>
> ...
>>   ...
>>
>> Fixes: 410f03831 ("sctp: add routing output fallback")
>> Fixes: 0ca50d12f ("sctp: fix src address selection if using secondary addresses")
>
> any syzbot references for this bug?
In Dmitry Vyukov mail, there was no syzbot reference provided.
Not sure if there's another way to tell syzbot.

> --
> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

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

[Dmitry Vyukov]

On Tue, Feb 6, 2018 at 6:06 AM, Xin Long <lucien.xin@gmail.com> wrote:
> On Tue, Feb 6, 2018 at 7:20 AM, David Ahern <dsahern@gmail.com> wrote:
>> On 2/5/18 12:48 PM, 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.
>>>
>> ...
>>>   ...
>>>
>>> Fixes: 410f03831 ("sctp: add routing output fallback")
>>> Fixes: 0ca50d12f ("sctp: fix src address selection if using secondary addresses")
>>
>> any syzbot references for this bug?
> In Dmitry Vyukov mail, there was no syzbot reference provided.
> Not sure if there's another way to tell syzbot.


If we are talking about "net: hang in unregister_netdevice: waiting
for lo to become free":
https://groups.google.com/d/msg/syzkaller/-06_laheMF0/xqezy58kAwAJ
Then there is no syzbot tag. It was found with syzkaller, but not
reported by syzbot because the manifestation is too tricky, it could
have been reported as "no output from test machine" with no additional
details, which is not too actionable.