3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "nikolay@redhat.com" <redacted>

[ Upstream commit e196c0e579902f42cf72414461fb034e5a1ffbf7 ]

Race between bonding_store_slaves_active() and slave manipulation
 functions. The bond_for_each_slave use in bonding_store_slaves_active()
 is not protected by any synchronization mechanism.
 NULL pointer dereference is easy to reach.
 Fixed by acquiring the bond->lock for the slave walk.

 v2: Make description text < 75 columns

Signed-off-by: Nikolay Aleksandrov <redacted>
Signed-off-by: Jay Vosburgh <redacted>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <redacted>
---
 drivers/net/bonding/bond_sysfs.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/bonding/bond_sysfs.c b/drivers/net/bonding/bond_sysfs.c
index 4ef7e2f..a03fde9 100644
--- a/drivers/net/bonding/bond_sysfs.c
+++ b/drivers/net/bonding/bond_sysfs.c

@@ -1579,6 +1579,7 @@ static ssize_t bonding_store_slaves_active(struct device *d,
 		goto out;
 	}
 
+	read_lock(&bond->lock);
 	bond_for_each_slave(bond, slave, i) {
 		if (!bond_is_active_slave(slave)) {
 			if (new_value)

@@ -1587,6 +1588,7 @@ static ssize_t bonding_store_slaves_active(struct device *d,
 				slave->inactive = 1;
 		}
 	}
+	read_unlock(&bond->lock);
 out:
 	return ret;
 }