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Date: Thu, 9 Jul 2015 13:54:58 -0300
From: Marcelo Ricardo Leitner <mleitner@...hat.com>
To: netdev@...r.kernel.org, linux-sctp@...r.kernel.org
Cc: Vlad Yasevich <vyasevich@...il.com>,
Neil Horman <nhorman@...driver.com>, tuexen@...muenster.de
Subject: Re: [RFC PATCH net-next] sctp: fix src address selection if using
secondary addresses
Cc'ing Michael too.
On Tue, Jul 07, 2015 at 02:42:25PM -0300, Marcelo Ricardo Leitner wrote:
> Hi folks,
>
> This is an attempt to better choose a src address for sctp packets as
> peers with rp_filter could be dropping our packets in some situations.
> With this patch, we try to respect and use a src address that belongs to
> the interface we are putting the packet out.
>
> I have that feeling that there is be a better way to do this, but I
> just couldn't see it.
>
> This patch has been tested with and without gateways between the peers
> and also just two peers connected via two subnets and results were
> pretty good.
>
> One could think that this limits the address combination we can use, but
> such combinations probably are just bogus anyway. Like, if you have an
> host with address A1 and B1 and another with A2 and B2, you cannot
> expect that A can use A1 to reach B2 through subnet B, because the
> return path would be via the other link which, when this switch happens,
> we are thinking it's broken.
>
> Thanks,
> Marcelo
>
> ---8<---
>
> In short, sctp is likely to incorrectly choose src address if socket is
> bound to secondary addresses. This patch fixes it by adding a new check
> that tries to anticipate if the src address would be expected by the
> next hop/peer on this interface by doing reverse routing.
>
> Also took the shot to reduce the indentation level on this code.
>
> Details:
>
> Currently, sctp will do a routing attempt without specifying the src
> address and compare the returned value (preferred source) with the
> addresses that the socket is bound to. When using secondary addresses,
> this will not match.
>
> Then it will try specifying each of the addresses that the socket is
> bound to and re-routing, checking if that address is valid as src for
> that dst. Thing is, this check alone is weak:
>
> # ip r l
> 192.168.100.0/24 dev eth1 proto kernel scope link src 192.168.100.149
> 192.168.122.0/24 dev eth0 proto kernel scope link src 192.168.122.147
>
> # ip a l
> 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default
> link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
> inet 127.0.0.1/8 scope host lo
> valid_lft forever preferred_lft forever
> inet6 ::1/128 scope host
> valid_lft forever preferred_lft forever
> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
> link/ether 52:54:00:15:18:6a brd ff:ff:ff:ff:ff:ff
> inet 192.168.122.147/24 brd 192.168.122.255 scope global dynamic eth0
> valid_lft 2160sec preferred_lft 2160sec
> inet 192.168.122.148/24 scope global secondary eth0
> valid_lft forever preferred_lft forever
> inet6 fe80::5054:ff:fe15:186a/64 scope link
> valid_lft forever preferred_lft forever
> 3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
> link/ether 52:54:00:b3:91:46 brd ff:ff:ff:ff:ff:ff
> inet 192.168.100.149/24 brd 192.168.100.255 scope global dynamic eth1
> valid_lft 2162sec preferred_lft 2162sec
> inet 192.168.100.148/24 scope global secondary eth1
> valid_lft forever preferred_lft forever
> inet6 fe80::5054:ff:feb3:9146/64 scope link
> valid_lft forever preferred_lft forever
> 4: ens9: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
> link/ether 52:54:00:05:47:ee brd ff:ff:ff:ff:ff:ff
> inet6 fe80::5054:ff:fe05:47ee/64 scope link
> valid_lft forever preferred_lft forever
>
> # ip r g 192.168.100.193 from 192.168.122.148
> 192.168.100.193 from 192.168.122.148 dev eth1
> cache
>
> Even if you specify an interface:
>
> # ip r g 192.168.100.193 from 192.168.122.148 oif eth1
> 192.168.100.193 from 192.168.122.148 dev eth1
> cache
>
> Although this would be valid, peers using rp_filter will drop such
> packets as their src doesn't match the routes for that interface.
>
> So we fix this by adding an extra check, we try to do the reverse
> routing and check if the interface used would be the same. If not, we
> skip such address. If yes, we use it.
>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
> ---
> net/sctp/protocol.c | 55 +++++++++++++++++++++++++++++++++++++++--------------
> 1 file changed, 41 insertions(+), 14 deletions(-)
>
> diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
> index 59e80356672bdf89777265ae1f8c384792dfb98c..e52fd6f77963426a7cf3e83ca01a9cdae1cb2c01 100644
> --- a/net/sctp/protocol.c
> +++ b/net/sctp/protocol.c
> @@ -53,6 +53,7 @@
> #include <net/net_namespace.h>
> #include <net/protocol.h>
> #include <net/ip.h>
> +#include <net/ip_fib.h>
> #include <net/ipv6.h>
> #include <net/route.h>
> #include <net/sctp/sctp.h>
> @@ -487,23 +488,49 @@ static void sctp_v4_get_dst(struct sctp_transport *t, union sctp_addr *saddr,
> */
> rcu_read_lock();
> list_for_each_entry_rcu(laddr, &bp->address_list, list) {
> + struct flowi4 in;
> + struct fib_result res;
> +
> if (!laddr->valid)
> continue;
> - if ((laddr->state == SCTP_ADDR_SRC) &&
> - (AF_INET == laddr->a.sa.sa_family)) {
> - fl4->fl4_sport = laddr->a.v4.sin_port;
> - flowi4_update_output(fl4,
> - asoc->base.sk->sk_bound_dev_if,
> - RT_CONN_FLAGS(asoc->base.sk),
> - daddr->v4.sin_addr.s_addr,
> - laddr->a.v4.sin_addr.s_addr);
> -
> - rt = ip_route_output_key(sock_net(sk), fl4);
> - if (!IS_ERR(rt)) {
> - dst = &rt->dst;
> - goto out_unlock;
> - }
> + if (laddr->state != SCTP_ADDR_SRC ||
> + AF_INET != laddr->a.sa.sa_family)
> + continue;
> +
> + fl4->fl4_sport = laddr->a.v4.sin_port;
> + flowi4_update_output(fl4,
> + asoc->base.sk->sk_bound_dev_if,
> + RT_CONN_FLAGS(asoc->base.sk),
> + daddr->v4.sin_addr.s_addr,
> + laddr->a.v4.sin_addr.s_addr);
> +
> + rt = ip_route_output_key(sock_net(sk), fl4);
> + if (IS_ERR(rt))
> + continue;
> +
> + dst = &rt->dst;
> +
> + /* Double check if this is really expected. We simulate
> + * rp_filter by swapping src and dst. If interfaces are
> + * different, means that this src wouldn't be expected
> + * by the other host on this interface.
> + */
> + memcpy(&in, fl4, sizeof(in));
> + in.daddr = fl4->saddr;
> + in.saddr = fl4->daddr;
> + in.flowi4_iif = fl4->flowi4_oif;
> + in.flowi4_oif = 0;
> +
> + if (fib_lookup(sock_net(sk), &in, &res) ||
> + res.type != RTN_LOCAL ||
> + fl4->flowi4_oif != FIB_RES_DEV(res)->ifindex) {
> + /* Failed, so this was a false hit */
> + dst_release(dst);
> + dst = NULL;
> + continue;
> }
> +
> + break;
> }
>
> out_unlock:
> --
> 2.4.1
>
> --
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