Subject: Re: [PATCH] net: bonding: avoid use-after-free with tx_hashtbl/rx_hashtbl

From: Jay Vosburgh <[email-masked]>
Date: Mon, 27 Mar 2023 21:38:04 -0700

sujing <[email-masked]> wrote:

>In bonding mode 6 (Balance-alb),
>there are some potential race conditions between the 'bond_close' process
>and the tx/rx processes that use tx_hashtbl/rx_hashtbl,
>which may lead to use-after-free.
>
>For instance, when the bond6 device is in the 'bond_close' process
>while some backlogged packets from upper level are transmitted
>to 'bond_start_xmit', there is a spinlock contention between
>'tlb_deinitialize' and 'tlb_choose_channel'.
>
>If 'tlb_deinitialize' preempts the lock before 'tlb_choose_channel',
>a NULL pointer kernel panic will be triggered.
>
>Here's the timeline:
>
>bond_close  ------------------  bond_start_xmit
>bond_alb_deinitialize  -------  __bond_start_xmit
>tlb_deinitialize  ------------  bond_alb_xmit
>spin_lock_bh  ----------------  bond_xmit_alb_slave_get
>tx_hashtbl = NULL  -----------  tlb_choose_channel
>spin_unlock_bh  --------------  //wait for spin_lock_bh
>------------------------------  spin_lock_bh
>------------------------------  __tlb_choose_channel
>causing kernel panic ========>  tx_hashtbl[hash_index].tx_slave
>------------------------------  spin_unlock_bh

	I'm still thinking on the race here, but have some questions
below about the implementation in the meantime.

>Signed-off-by: sujing <[email-masked]>
>---
> drivers/net/bonding/bond_alb.c  | 32 +++++++++------------------
> drivers/net/bonding/bond_main.c | 39 +++++++++++++++++++++++++++------
> include/net/bond_alb.h          |  5 ++++-
> 3 files changed, 46 insertions(+), 30 deletions(-)
>
>diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
>index b9dbad3a8af8..f6ff5ea835c4 100644
>--- a/drivers/net/bonding/bond_alb.c
>+++ b/drivers/net/bonding/bond_alb.c
>@@ -71,7 +71,7 @@ static inline u8 _simple_hash(const u8 *hash_start, int hash_size)
> 
> /*********************** tlb specific functions ***************************/
> 
>-static inline void tlb_init_table_entry(struct tlb_client_info *entry, int save_load)
>+void tlb_init_table_entry(struct tlb_client_info *entry, int save_load)
> {
> 	if (save_load) {
> 		entry->load_history = 1 + entry->tx_bytes /
>@@ -269,8 +269,8 @@ static void rlb_update_entry_from_arp(struct bonding *bond, struct arp_pkt *arp)
> 	spin_unlock_bh(&bond->mode_lock);
> }
> 
>-static int rlb_arp_recv(const struct sk_buff *skb, struct bonding *bond,
>-			struct slave *slave)
>+int rlb_arp_recv(const struct sk_buff *skb, struct bonding *bond,
>+		 struct slave *slave)
> {
> 	struct arp_pkt *arp, _arp;
> 
>@@ -756,7 +756,7 @@ static void rlb_init_table_entry_src(struct rlb_client_info *entry)
> 	entry->src_next = RLB_NULL_INDEX;
> }
> 
>-static void rlb_init_table_entry(struct rlb_client_info *entry)
>+void rlb_init_table_entry(struct rlb_client_info *entry)
> {
> 	memset(entry, 0, sizeof(struct rlb_client_info));
> 	rlb_init_table_entry_dst(entry);
>@@ -874,9 +874,6 @@ static int rlb_initialize(struct bonding *bond)
> 
> 	spin_unlock_bh(&bond->mode_lock);
> 
>-	/* register to receive ARPs */
>-	bond->recv_probe = rlb_arp_recv;
>-
> 	return 0;
> }
> 
>@@ -888,7 +885,6 @@ static void rlb_deinitialize(struct bonding *bond)
> 
> 	kfree(bond_info->rx_hashtbl);
> 	bond_info->rx_hashtbl = NULL;
>-	bond_info->rx_hashtbl_used_head = RLB_NULL_INDEX;

	Why remove this line?

> 	spin_unlock_bh(&bond->mode_lock);
> }
>@@ -1303,7 +1299,7 @@ static bool alb_determine_nd(struct sk_buff *skb, struct bonding *bond)
> 
> /************************ exported alb functions ************************/
> 
>-int bond_alb_initialize(struct bonding *bond, int rlb_enabled)
>+int bond_alb_initialize(struct bonding *bond)
> {
> 	int res;
> 
>@@ -1311,15 +1307,10 @@ int bond_alb_initialize(struct bonding *bond, int rlb_enabled)
> 	if (res)
> 		return res;
> 
>-	if (rlb_enabled) {
>-		res = rlb_initialize(bond);
>-		if (res) {
>-			tlb_deinitialize(bond);
>-			return res;
>-		}
>-		bond->alb_info.rlb_enabled = 1;
>-	} else {
>-		bond->alb_info.rlb_enabled = 0;
>+	res = rlb_initialize(bond);
>+	if (res) {
>+		tlb_deinitialize(bond);
>+		return res;
> 	}
> 
> 	return 0;
>@@ -1327,12 +1318,9 @@ int bond_alb_initialize(struct bonding *bond, int rlb_enabled)
> 
> void bond_alb_deinitialize(struct bonding *bond)
> {
>-	struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
>-
> 	tlb_deinitialize(bond);
> 
>-	if (bond_info->rlb_enabled)
>-		rlb_deinitialize(bond);
>+	rlb_deinitialize(bond);

	Why is rlb_deinitialize() now unconditionally called here and in
bond_alb_initialize()?  if rlb_enabled is false, why set up / tear down
the RLB hash table that won't be used?

> }
> 
> static netdev_tx_t bond_do_alb_xmit(struct sk_buff *skb, struct bonding *bond,
>diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>index 236e5219c811..8fcb5d3ac0a2 100644
>--- a/drivers/net/bonding/bond_main.c
>+++ b/drivers/net/bonding/bond_main.c
>@@ -4217,6 +4217,7 @@ static int bond_open(struct net_device *bond_dev)
> 	struct bonding *bond = netdev_priv(bond_dev);
> 	struct list_head *iter;
> 	struct slave *slave;
>+	int i;
> 
> 	if (BOND_MODE(bond) == BOND_MODE_ROUNDROBIN && !bond->rr_tx_counter) {
> 		bond->rr_tx_counter = alloc_percpu(u32);
>@@ -4239,11 +4240,29 @@ static int bond_open(struct net_device *bond_dev)
> 	}
> 
> 	if (bond_is_lb(bond)) {
>-		/* bond_alb_initialize must be called before the timer
>-		 * is started.
>-		 */
>-		if (bond_alb_initialize(bond, (BOND_MODE(bond) == BOND_MODE_ALB)))
>-			return -ENOMEM;
>+		struct alb_bond_info *bond_info = &(BOND_ALB_INFO(bond));
>+
>+		spin_lock_bh(&bond->mode_lock);
>+
>+		for (i = 0; i < TLB_HASH_TABLE_SIZE; i++)
>+			tlb_init_table_entry(&bond_info->tx_hashtbl[i], 0);
>+
>+		spin_unlock_bh(&bond->mode_lock);
>+
>+		if (BOND_MODE(bond) == BOND_MODE_ALB) {
>+			bond->alb_info.rlb_enabled = 1;
>+			spin_lock_bh(&bond->mode_lock);
>+
>+			bond_info->rx_hashtbl_used_head = RLB_NULL_INDEX;
>+			for (i = 0; i < RLB_HASH_TABLE_SIZE; i++)
>+				rlb_init_table_entry(bond_info->rx_hashtbl + i);
>+
>+			spin_unlock_bh(&bond->mode_lock);
>+			bond->recv_probe = rlb_arp_recv;
>+		} else {
>+			bond->alb_info.rlb_enabled = 0;
>+		}
>+

	Why is all of the above done directly in bond_open() and not in
bond_alb.c somewhere?  That would reduce some churn (changing some
functions away from static).

	Also, I see that bond_alb_initialize() is now called from
bond_init() instead of bond_open(), and it only calls rlb_initialize().
However, this now duplicates most of the functionality of
rlb_initialize() and tlb_initialize() here.  Why?

	In general, the described race is TX vs. close processing, so
why is there so much change to the open processing?

	-J

> 		if (bond->params.tlb_dynamic_lb || BOND_MODE(bond) == BOND_MODE_ALB)
> 			queue_delayed_work(bond->wq, &bond->alb_work, 0);
> 	}
>@@ -4279,8 +4298,6 @@ static int bond_close(struct net_device *bond_dev)
> 
> 	bond_work_cancel_all(bond);
> 	bond->send_peer_notif = 0;
>-	if (bond_is_lb(bond))
>-		bond_alb_deinitialize(bond);
> 	bond->recv_probe = NULL;
> 
> 	if (bond_uses_primary(bond)) {
>@@ -5854,6 +5871,8 @@ static void bond_uninit(struct net_device *bond_dev)
> 	struct list_head *iter;
> 	struct slave *slave;
> 
>+	bond_alb_deinitialize(bond);
>+
> 	bond_netpoll_cleanup(bond_dev);
> 
> 	/* Release the bonded slaves */
>@@ -6295,6 +6314,12 @@ static int bond_init(struct net_device *bond_dev)
> 	    bond_dev->addr_assign_type == NET_ADDR_PERM)
> 		eth_hw_addr_random(bond_dev);
> 
>+	/* bond_alb_initialize must be called before the timer
>+	 * is started.
>+	 */
>+	if (bond_alb_initialize(bond))
>+		return -ENOMEM;
>+
> 	return 0;
> }
> 
>diff --git a/include/net/bond_alb.h b/include/net/bond_alb.h
>index 9dc082b2d543..9fd16e20ef82 100644
>--- a/include/net/bond_alb.h
>+++ b/include/net/bond_alb.h
>@@ -150,7 +150,7 @@ struct alb_bond_info {
> 						 */
> };
> 
>-int bond_alb_initialize(struct bonding *bond, int rlb_enabled);
>+int bond_alb_initialize(struct bonding *bond);
> void bond_alb_deinitialize(struct bonding *bond);
> int bond_alb_init_slave(struct bonding *bond, struct slave *slave);
> void bond_alb_deinit_slave(struct bonding *bond, struct slave *slave);
>@@ -165,5 +165,8 @@ struct slave *bond_xmit_tlb_slave_get(struct bonding *bond,
> void bond_alb_monitor(struct work_struct *);
> int bond_alb_set_mac_address(struct net_device *bond_dev, void *addr);
> void bond_alb_clear_vlan(struct bonding *bond, unsigned short vlan_id);
>+int rlb_arp_recv(const struct sk_buff *skb, struct bonding *bond, struct slave *slave);
>+void tlb_init_table_entry(struct tlb_client_info *entry, int save_load);
>+void rlb_init_table_entry(struct rlb_client_info *entry);
> #endif /* _NET_BOND_ALB_H */
> 
>-- 
>2.27.0
>

---
	-Jay Vosburgh, [email-masked]