From 4f5474e7fd68988cb11373fc698bf10b35b49e31 Mon Sep 17 00:00:00 2001 From: Nikolay Aleksandrov Date: Wed, 12 Jun 2013 00:07:02 +0200 Subject: [PATCH] bonding: fix igmp_retrans type and two related races First the type of igmp_retrans (which is the actual counter of igmp_resend parameter) is changed to u8 to be able to store values up to 255 (as per documentation). There are two races that were hidden there and which are easy to trigger after the previous fix, the first is between bond_resend_igmp_join_requests and bond_change_active_slave where igmp_retrans is set and can be altered by the periodic. The second race condition is between multiple running instances of the periodic (upon execution it can be scheduled again for immediate execution which can cause the counter to go < 0 which in the unsigned case leads to unnecessary igmp retransmissions). Since in bond_change_active_slave bond->lock is held for reading and curr_slave_lock for writing, we use curr_slave_lock for mutual exclusion. We can't drop them as there're cases where RTNL is not held when bond_change_active_slave is called. RCU is unlocked in bond_resend_igmp_join_requests before getting curr_slave_lock since we don't need it there and it's pointless to delay. The decrement is moved inside the "if" block because if we decrement unconditionally there's still a possibility for a race condition although it is much more difficult to hit (many changes have to happen in a very short period in order to trigger) which in the case of 3 parallel running instances of this function and igmp_retrans == 1 (with check bond->igmp_retrans-- > 1) is: f1 passes, doesn't re-schedule, but decrements - igmp_retrans = 0 f2 then passes, doesn't re-schedule, but decrements - igmp_retrans = 255 f3 does the unnecessary retransmissions. Signed-off-by: Nikolay Aleksandrov Signed-off-by: Jay Vosburgh Signed-off-by: David S. Miller --- drivers/net/bonding/bond_main.c | 19 +++++++++++++------ drivers/net/bonding/bonding.h | 2 +- 2 files changed, 14 insertions(+), 7 deletions(-) diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c index 473633ab5f56..02d9ae7d527e 100644 --- a/drivers/net/bonding/bond_main.c +++ b/drivers/net/bonding/bond_main.c @@ -764,8 +764,8 @@ static void bond_resend_igmp_join_requests(struct bonding *bond) struct net_device *bond_dev, *vlan_dev, *upper_dev; struct vlan_entry *vlan; - rcu_read_lock(); read_lock(&bond->lock); + rcu_read_lock(); bond_dev = bond->dev; @@ -787,12 +787,19 @@ static void bond_resend_igmp_join_requests(struct bonding *bond) if (vlan_dev) __bond_resend_igmp_join_requests(vlan_dev); } - - if (--bond->igmp_retrans > 0) - queue_delayed_work(bond->wq, &bond->mcast_work, HZ/5); - - read_unlock(&bond->lock); rcu_read_unlock(); + + /* We use curr_slave_lock to protect against concurrent access to + * igmp_retrans from multiple running instances of this function and + * bond_change_active_slave + */ + write_lock_bh(&bond->curr_slave_lock); + if (bond->igmp_retrans > 1) { + bond->igmp_retrans--; + queue_delayed_work(bond->wq, &bond->mcast_work, HZ/5); + } + write_unlock_bh(&bond->curr_slave_lock); + read_unlock(&bond->lock); } static void bond_resend_igmp_join_requests_delayed(struct work_struct *work) diff --git a/drivers/net/bonding/bonding.h b/drivers/net/bonding/bonding.h index 2baec24388b1..f989e1529a29 100644 --- a/drivers/net/bonding/bonding.h +++ b/drivers/net/bonding/bonding.h @@ -225,7 +225,7 @@ struct bonding { rwlock_t curr_slave_lock; u8 send_peer_notif; s8 setup_by_slave; - s8 igmp_retrans; + u8 igmp_retrans; #ifdef CONFIG_PROC_FS struct proc_dir_entry *proc_entry; char proc_file_name[IFNAMSIZ];