bonding: fix race condition in bonding_store_slaves_active

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 <nikolay@redhat.com>
Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/net/bonding/bond_sysfs.c b/drivers/net/bonding/bond_sysfs.c
index 3327a072e224..1877ed7ca086 100644
--- a/drivers/net/bonding/bond_sysfs.c
+++ b/drivers/net/bonding/bond_sysfs.c
@@ -1568,6 +1568,7 @@ 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)
@@ -1576,6 +1577,7 @@ static ssize_t bonding_store_slaves_active(struct device *d,
                                 slave->inactive = 1;
                 }
         }
+        read_unlock(&bond->lock);
 out:
         return ret;
 }