ipv6: anycast: complete RCU handling of struct ifacaddr6

struct ifacaddr6 are already freed after RCU grace period.

Add __rcu qualifier to aca_next pointer, and idev->ac_list

Add relevant rcu_assign_pointer() and dereference accessors.

ipv6_chk_acast_dev() no longer needs to acquire idev->lock.

/proc/net/anycast6 is now purely RCU protected, it no
longer acquires idev->lock.

Similarly in6_dump_addrs() can use RCU protection to iterate
through anycast addresses. It was relying on a mixture of RCU
and RTNL but next patches will get rid of RTNL there.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20240223201054.220534-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/if_inet6.h

@@ -144,7 +144,7 @@ struct ipv6_ac_socklist {
 struct ifacaddr6 {
 	struct in6_addr		aca_addr;
 	struct fib6_info	*aca_rt;
-	struct ifacaddr6	*aca_next;
+	struct ifacaddr6 __rcu	*aca_next;
 	struct hlist_node	aca_addr_lst;
 	int			aca_users;
 	refcount_t		aca_refcnt;
@@ -196,7 +196,7 @@ struct inet6_dev {
 	spinlock_t		mc_report_lock;	/* mld query report lock */
 	struct mutex		mc_lock;	/* mld global lock */
 
-	struct ifacaddr6	*ac_list;
+	struct ifacaddr6 __rcu	*ac_list;
 	rwlock_t		lock;
 	refcount_t		refcnt;
 	__u32			if_flags;

net/ipv6/addrconf.c

@@ -5314,8 +5314,8 @@ static int in6_dump_addrs(struct inet6_dev *idev, struct sk_buff *skb,
 	case ANYCAST_ADDR:
 		fillargs->event = RTM_GETANYCAST;
 		/* anycast address */
-		for (ifaca = idev->ac_list; ifaca;
-		     ifaca = ifaca->aca_next, ip_idx++) {
+		for (ifaca = rcu_dereference(idev->ac_list); ifaca;
+		     ifaca = rcu_dereference(ifaca->aca_next), ip_idx++) {
 			if (ip_idx < s_ip_idx)
 				continue;
 			err = inet6_fill_ifacaddr(skb, ifaca, fillargs);

net/ipv6/anycast.c

@@ -296,7 +296,8 @@ int __ipv6_dev_ac_inc(struct inet6_dev *idev, const struct in6_addr *addr)
 		goto out;
 	}
 
-	for (aca = idev->ac_list; aca; aca = aca->aca_next) {
+	for (aca = rtnl_dereference(idev->ac_list); aca;
+	     aca = rtnl_dereference(aca->aca_next)) {
 		if (ipv6_addr_equal(&aca->aca_addr, addr)) {
 			aca->aca_users++;
 			err = 0;
@@ -317,13 +318,13 @@ int __ipv6_dev_ac_inc(struct inet6_dev *idev, const struct in6_addr *addr)
 		goto out;
 	}
 
-	aca->aca_next = idev->ac_list;
-	idev->ac_list = aca;
-
 	/* Hold this for addrconf_join_solict() below before we unlock,
 	 * it is already exposed via idev->ac_list.
 	 */
 	aca_get(aca);
+	aca->aca_next = idev->ac_list;
+	rcu_assign_pointer(idev->ac_list, aca);
+
 	write_unlock_bh(&idev->lock);
 
 	ipv6_add_acaddr_hash(net, aca);
@@ -350,7 +351,8 @@ int __ipv6_dev_ac_dec(struct inet6_dev *idev, const struct in6_addr *addr)
 
 	write_lock_bh(&idev->lock);
 	prev_aca = NULL;
-	for (aca = idev->ac_list; aca; aca = aca->aca_next) {
+	for (aca = rtnl_dereference(idev->ac_list); aca;
+	     aca = rtnl_dereference(aca->aca_next)) {
 		if (ipv6_addr_equal(&aca->aca_addr, addr))
 			break;
 		prev_aca = aca;
@@ -364,9 +366,9 @@ int __ipv6_dev_ac_dec(struct inet6_dev *idev, const struct in6_addr *addr)
 		return 0;
 	}
 	if (prev_aca)
-		prev_aca->aca_next = aca->aca_next;
+		rcu_assign_pointer(prev_aca->aca_next, aca->aca_next);
 	else
-		idev->ac_list = aca->aca_next;
+		rcu_assign_pointer(idev->ac_list, aca->aca_next);
 	write_unlock_bh(&idev->lock);
 	ipv6_del_acaddr_hash(aca);
 	addrconf_leave_solict(idev, &aca->aca_addr);
@@ -392,8 +394,8 @@ void ipv6_ac_destroy_dev(struct inet6_dev *idev)
 	struct ifacaddr6 *aca;
 
 	write_lock_bh(&idev->lock);
-	while ((aca = idev->ac_list) != NULL) {
-		idev->ac_list = aca->aca_next;
+	while ((aca = rtnl_dereference(idev->ac_list)) != NULL) {
+		rcu_assign_pointer(idev->ac_list, aca->aca_next);
 		write_unlock_bh(&idev->lock);
 
 		ipv6_del_acaddr_hash(aca);
@@ -420,11 +422,10 @@ static bool ipv6_chk_acast_dev(struct net_device *dev, const struct in6_addr *ad
 
 	idev = __in6_dev_get(dev);
 	if (idev) {
-		read_lock_bh(&idev->lock);
-		for (aca = idev->ac_list; aca; aca = aca->aca_next)
+		for (aca = rcu_dereference(idev->ac_list); aca;
+		     aca = rcu_dereference(aca->aca_next))
 			if (ipv6_addr_equal(&aca->aca_addr, addr))
 				break;
-		read_unlock_bh(&idev->lock);
 		return aca != NULL;
 	}
 	return false;
@@ -477,30 +478,25 @@ bool ipv6_chk_acast_addr_src(struct net *net, struct net_device *dev,
 struct ac6_iter_state {
 	struct seq_net_private p;
 	struct net_device *dev;
-	struct inet6_dev *idev;
 };
 
 #define ac6_seq_private(seq)	((struct ac6_iter_state *)(seq)->private)
 
 static inline struct ifacaddr6 *ac6_get_first(struct seq_file *seq)
 {
-	struct ifacaddr6 *im = NULL;
 	struct ac6_iter_state *state = ac6_seq_private(seq);
 	struct net *net = seq_file_net(seq);
+	struct ifacaddr6 *im = NULL;
 
-	state->idev = NULL;
 	for_each_netdev_rcu(net, state->dev) {
 		struct inet6_dev *idev;
+
 		idev = __in6_dev_get(state->dev);
 		if (!idev)
 			continue;
-		read_lock_bh(&idev->lock);
-		im = idev->ac_list;
-		if (im) {
-			state->idev = idev;
+		im = rcu_dereference(idev->ac_list);
+		if (im)
 			break;
-		}
-		read_unlock_bh(&idev->lock);
 	}
 	return im;
 }
@@ -508,22 +504,17 @@ static inline struct ifacaddr6 *ac6_get_first(struct seq_file *seq)
 static struct ifacaddr6 *ac6_get_next(struct seq_file *seq, struct ifacaddr6 *im)
 {
 	struct ac6_iter_state *state = ac6_seq_private(seq);
+	struct inet6_dev *idev;
 
-	im = im->aca_next;
+	im = rcu_dereference(im->aca_next);
 	while (!im) {
-		if (likely(state->idev != NULL))
-			read_unlock_bh(&state->idev->lock);
-
 		state->dev = next_net_device_rcu(state->dev);
-		if (!state->dev) {
-			state->idev = NULL;
+		if (!state->dev)
 			break;
-		}
-		state->idev = __in6_dev_get(state->dev);
-		if (!state->idev)
+		idev = __in6_dev_get(state->dev);
+		if (!idev)
 			continue;
-		read_lock_bh(&state->idev->lock);
-		im = state->idev->ac_list;
+		im = rcu_dereference(idev->ac_list);
 	}
 	return im;
 }
@@ -555,12 +546,6 @@ static void *ac6_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 static void ac6_seq_stop(struct seq_file *seq, void *v)
 	__releases(RCU)
 {
-	struct ac6_iter_state *state = ac6_seq_private(seq);
-
-	if (likely(state->idev != NULL)) {
-		read_unlock_bh(&state->idev->lock);
-		state->idev = NULL;
-	}
 	rcu_read_unlock();
 }