packets: Always register packet sk in the same order

BugLink: https://bugs.launchpad.net/bugs/1838116
[ Upstream commit a4dc6a49156b1f8d6e17251ffda17c9e6a5db78a ]

When using fanouts with AF_PACKET, the demux functions such as
fanout_demux_cpu will return an index in the fanout socket array, which
corresponds to the selected socket.

The ordering of this array depends on the order the sockets were added
to a given fanout group, so for FANOUT_CPU this means sockets are bound
to cpus in the order they are configured, which is OK.

However, when stopping then restarting the interface these sockets are
bound to, the sockets are reassigned to the fanout group in the reverse
order, due to the fact that they were inserted at the head of the
interface's AF_PACKET socket list.

This means that traffic that was directed to the first socket in the
fanout group is now directed to the last one after an interface restart.

In the case of FANOUT_CPU, traffic from CPU0 will be directed to the
socket that used to receive traffic from the last CPU after an interface
restart.

This commit introduces a helper to add a socket at the tail of a list,
then uses it to register AF_PACKET sockets.

Note that this changes the order in which sockets are listed in /proc and
with sock_diag.

Fixes: dc99f600698d ("packet: Add fanout support")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/include/net/sock.h b/include/net/sock.h
index 813912810f5e2404b3804f1c0870995838a04d44..30d3c67984e13f21ab12921843dc0918605c666b 100644 (file)
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -687,6 +687,12 @@ static inline void sk_add_node_rcu(struct sock *sk, struct hlist_head *list)
                hlist_add_head_rcu(&sk->sk_node, list);
 }
 
+static inline void sk_add_node_tail_rcu(struct sock *sk, struct hlist_head *list)
+{
+       sock_hold(sk);
+       hlist_add_tail_rcu(&sk->sk_node, list);
+}
+
 static inline void __sk_nulls_add_node_rcu(struct sock *sk, struct hlist_nulls_head *list)
 {
        hlist_nulls_add_head_rcu(&sk->sk_nulls_node, list);

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index a6caf8614329408288024a99f29539db2bc1e83c..8f8aa68824016a1cfcbc1702642c057126946133 100644 (file)
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3272,7 +3272,7 @@ static int packet_create(struct net *net, struct socket *sock, int protocol,
        }
 
        mutex_lock(&net->packet.sklist_lock);
-       sk_add_node_rcu(sk, &net->packet.sklist);
+       sk_add_node_tail_rcu(sk, &net->packet.sklist);
        mutex_unlock(&net->packet.sklist_lock);
 
        preempt_disable();