Subject: Re: [PATCH net] bonding: fix bond_arp_rcv() race of curr_active_slave

From: Veaceslav Falico <[email-masked]>
Date: Thu, 20 Feb 2014 12:15:19 +0100

On Thu, Feb 20, 2014 at 12:07:57PM +0100, Veaceslav Falico wrote:
>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 <[email-masked]>
>Fixes: aeea64a ("bonding: don't trust arp requests unless active slave really works")
>CC: Jay Vosburgh <[email-masked]>
>CC: Andy Gospodarek <[email-masked]>
>Signed-off-by: Veaceslav Falico <[email-masked]>

Sorry David, it should have been net-next (I've based it on the net-next
tree).

Can you apply it to net-next or should I resend it?

Sorry for the noise.

>---
> drivers/net/bonding/bond_main.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
>diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>index 71edf03..bd70bbc 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:
>-- 
>1.8.4
>