bonding: fix bond_arp_rcv() race of curr_active_slave

bond->curr_active_slave can be changed between its deferences, even to
NULL, and thus we might panic.

We're always holding the rcu (rx_handler->bond_handle_frame()->bond_arp_rcv())
so fix this by rcu_dereferencing() it and using the saved.

Reported-by: Ding Tianhong <dingtianhong@huawei.com>
Fixes: aeea64a ("bonding: don't trust arp requests unless active slave really works")
CC: Jay Vosburgh <fubar@us.ibm.com>
CC: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
Acked-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 3 deletions

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 71edf03544aa..bd70bbc7992c 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2254,6 +2254,7 @@ int bond_arp_rcv(const struct sk_buff *skb, struct bonding *bond,
                  struct slave *slave)
 {
         struct arphdr *arp = (struct arphdr *)skb->data;
+        struct slave *curr_active_slave;
         unsigned char *arp_ptr;
         __be32 sip, tip;
         int alen, is_arp = skb->protocol == __cpu_to_be16(ETH_P_ARP);
@@ -2299,6 +2300,8 @@ int bond_arp_rcv(const struct sk_buff *skb, struct bonding *bond,
                  bond->params.arp_validate, slave_do_arp_validate(bond, slave),
                  &sip, &tip);
 
+        curr_active_slave = rcu_dereference(bond->curr_active_slave);
+
         /*
          * Backup slaves won't see the ARP reply, but do come through
          * here for each ARP probe (so we swap the sip/tip to validate
@@ -2312,11 +2315,12 @@ int bond_arp_rcv(const struct sk_buff *skb, struct bonding *bond,
          * is done to avoid endless looping when we can't reach the
          * arp_ip_target and fool ourselves with our own arp requests.
          */
+
         if (bond_is_active_slave(slave))
                 bond_validate_arp(bond, slave, sip, tip);
-        else if (bond->curr_active_slave &&
-                 time_after(slave_last_rx(bond, bond->curr_active_slave),
-                            bond->curr_active_slave->last_link_up))
+        else if (curr_active_slave &&
+                 time_after(slave_last_rx(bond, curr_active_slave),
+                            curr_active_slave->last_link_up))
                 bond_validate_arp(bond, slave, tip, sip);
 
 out_unlock: