Subject: Re: [PATCH net-next v2 6/6] bonding: Fix multiple long standing offload races

From: Hangbin Liu <[email-masked]>
Date: Thu, 10 Apr 2025 03:07:26 +0000

On Wed, Apr 09, 2025 at 05:41:33PM +0300, Cosmin Ratiu wrote:
> Refactor the bonding ipsec offload operations to fix a number of
> long-standing control plane races between state migration and user
> deletion and a few other issues.
> 
> xfrm state deletion can happen concurrently with
> bond_change_active_slave() operation. This manifests itself as a
> bond_ipsec_del_sa() call with x->lock held, followed by a
> bond_ipsec_free_sa() a bit later from a wq. The alternate path of
> these calls coming from xfrm_dev_state_flush() can't happen, as that
> needs the RTNL lock and bond_change_active_slave() already holds it.
> 
> 1. bond_ipsec_del_sa_all() might call xdo_dev_state_delete() a second
>    time on an xfrm state that was concurrently killed. This is bad.
> 2. bond_ipsec_add_sa_all() can add a state on the new device, but
>    pending bond_ipsec_free_sa() calls from the old device will then hit
>    the WARN_ON() and then, worse, call xdo_dev_state_free() on the new
>    device without a corresponding xdo_dev_state_delete().
> 3. Resolve a sleeping in atomic context introduced by the mentioned
>    "Fixes" commit.
> 
> bond_ipsec_del_sa_all() and bond_ipsec_add_sa_all() now acquire x->lock
> and check for x->km.state to help with problems 1 and 2. And since
> xso.real_dev is now a private pointer managed by the bonding driver in
> xfrm state, make better use of it to fully fix problems 1 and 2. In
> bond_ipsec_del_sa_all(), set xso.real_dev to NULL while holding both the
> mutex and x->lock, which makes sure that neither bond_ipsec_del_sa() nor
> bond_ipsec_free_sa() could run concurrently.
> 
> Fix problem 3 by moving the list cleanup (which requires the mutex) from
> bond_ipsec_del_sa() (called from atomic context) to bond_ipsec_free_sa()
> 
> Finally, simplify bond_ipsec_del_sa() and bond_ipsec_free_sa() by using
> xso->real_dev directly, since it's now protected by locks and can be
> trusted to always reflect the offload device.
> 
> Fixes: 2aeeef906d5a ("bonding: change ipsec_lock from spin lock to mutex")
> Signed-off-by: Cosmin Ratiu <[email-masked]>
> Reviewed-by: Leon Romanovsky <[email-masked]>
> ---
>  drivers/net/bonding/bond_main.c | 76 ++++++++++++++++-----------------
>  1 file changed, 36 insertions(+), 40 deletions(-)
> 
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 14f7c9712ad4..78e1d5274a45 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -545,7 +545,20 @@ static void bond_ipsec_add_sa_all(struct bonding *bond)
>  			slave_warn(bond_dev, real_dev, "%s: failed to add SA\n", __func__);
>  			continue;
>  		}
> +
> +		spin_lock_bh(&ipsec->xs->lock);
> +		/* xs might have been killed by the user during the migration
> +		 * to the new dev, but bond_ipsec_del_sa() should have done
> +		 * nothing, as xso.real_dev is NULL.
> +		 * Delete it from the device we just added it to. The pending
> +		 * bond_ipsec_free_sa() call will do the rest of the cleanup.
> +		 */
> +		if (ipsec->xs->km.state == XFRM_STATE_DEAD &&
> +		    real_dev->xfrmdev_ops->xdo_dev_state_delete)
> +			real_dev->xfrmdev_ops->xdo_dev_state_delete(real_dev,
> +								    ipsec->xs);
>  		ipsec->xs->xso.real_dev = real_dev;
> +		spin_unlock_bh(&ipsec->xs->lock);
>  	}
>  out:
>  	mutex_unlock(&bond->ipsec_lock);
> @@ -560,48 +573,26 @@ static void bond_ipsec_del_sa(struct net_device *bond_dev,
>  			      struct xfrm_state *xs)
>  {
>  	struct net_device *real_dev;
> -	netdevice_tracker tracker;
> -	struct bond_ipsec *ipsec;
>  	struct bonding *bond;
> -	struct slave *slave;
>  
>  	if (!bond_dev)
>  		return;
>  
> -	rcu_read_lock();
>  	bond = netdev_priv(bond_dev);

The bond is not used in bond_ipsec_del_sa() any more. You can remove it too.

> -	slave = rcu_dereference(bond->curr_active_slave);
> -	real_dev = slave ? slave->dev : NULL;
> -	netdev_hold(real_dev, &tracker, GFP_ATOMIC);
> -	rcu_read_unlock();
> -
> -	if (!slave)
> -		goto out;
>  
>  	if (!xs->xso.real_dev)
> -		goto out;
> +		return;
>  
> -	WARN_ON(xs->xso.real_dev != real_dev);
> +	real_dev = xs->xso.real_dev;
>  
>  	if (!real_dev->xfrmdev_ops ||
>  	    !real_dev->xfrmdev_ops->xdo_dev_state_delete ||
>  	    netif_is_bond_master(real_dev)) {
>  		slave_warn(bond_dev, real_dev, "%s: no slave xdo_dev_state_delete\n", __func__);
> -		goto out;
> +		return;
>  	}
>  
>  	real_dev->xfrmdev_ops->xdo_dev_state_delete(real_dev, xs);
> -out:
> -	netdev_put(real_dev, &tracker);
> -	mutex_lock(&bond->ipsec_lock);
> -	list_for_each_entry(ipsec, &bond->ipsec_list, list) {
> -		if (ipsec->xs == xs) {
> -			list_del(&ipsec->list);
> -			kfree(ipsec);
> -			break;
> -		}
> -	}
> -	mutex_unlock(&bond->ipsec_lock);
>  }

Thanks
Hangbin