neighbour: Convert RTM_GETNEIGHTBL to RCU.

neightbl_dump_info() calls these functions for each neigh_tables[]
entry:

  1. neightbl_fill_info() for tbl->parms
  2. neightbl_fill_param_info() for tbl->parms_list (except tbl->parms)

Both functions rely on the table lock (read_lock_bh(&tbl->lock))
and RTNL is not needed.

Let's fetch the table under RCU and convert RTM_GETNEIGHTBL to RCU.

Note that the first entry of tbl->parms_list is tbl->parms.list and
embedded in neigh_table, so list_next_entry() is safe.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20251022054004.2514876-4-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 9 insertions, 14 deletions

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 5bbebbfcba43..a660723476fd 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -2176,7 +2176,7 @@ static int neightbl_fill_parms(struct sk_buff *skb, struct neigh_parms *parms)
 		return -ENOBUFS;
 
 	if ((parms->dev &&
-	     nla_put_u32(skb, NDTPA_IFINDEX, parms->dev->ifindex)) ||
+	     nla_put_u32(skb, NDTPA_IFINDEX, READ_ONCE(parms->dev->ifindex))) ||
 	    nla_put_u32(skb, NDTPA_REFCNT, refcount_read(&parms->refcnt)) ||
 	    nla_put_u32(skb, NDTPA_QUEUE_LENBYTES,
 			NEIGH_VAR(parms, QUEUE_LEN_BYTES)) ||
@@ -2228,8 +2228,6 @@ static int neightbl_fill_info(struct sk_buff *skb, struct neigh_table *tbl,
 		return -EMSGSIZE;
 
 	ndtmsg = nlmsg_data(nlh);
-
-	read_lock_bh(&tbl->lock);
 	ndtmsg->ndtm_family = tbl->family;
 	ndtmsg->ndtm_pad1   = 0;
 	ndtmsg->ndtm_pad2   = 0;
@@ -2255,11 +2253,9 @@ static int neightbl_fill_info(struct sk_buff *skb, struct neigh_table *tbl,
 			.ndtc_proxy_qlen	= READ_ONCE(tbl->proxy_queue.qlen),
 		};
 
-		rcu_read_lock();
 		nht = rcu_dereference(tbl->nht);
 		ndc.ndtc_hash_rnd = nht->hash_rnd[0];
 		ndc.ndtc_hash_mask = ((1 << nht->hash_shift) - 1);
-		rcu_read_unlock();
 
 		if (nla_put(skb, NDTA_CONFIG, sizeof(ndc), &ndc))
 			goto nla_put_failure;
@@ -2297,12 +2293,10 @@ static int neightbl_fill_info(struct sk_buff *skb, struct neigh_table *tbl,
 	if (neightbl_fill_parms(skb, &tbl->parms) < 0)
 		goto nla_put_failure;
 
-	read_unlock_bh(&tbl->lock);
 	nlmsg_end(skb, nlh);
 	return 0;
 
 nla_put_failure:
-	read_unlock_bh(&tbl->lock);
 	nlmsg_cancel(skb, nlh);
 	return -EMSGSIZE;
 }
@@ -2321,8 +2315,6 @@ static int neightbl_fill_param_info(struct sk_buff *skb,
 		return -EMSGSIZE;
 
 	ndtmsg = nlmsg_data(nlh);
-
-	read_lock_bh(&tbl->lock);
 	ndtmsg->ndtm_family = tbl->family;
 	ndtmsg->ndtm_pad1   = 0;
 	ndtmsg->ndtm_pad2   = 0;
@@ -2331,11 +2323,9 @@ static int neightbl_fill_param_info(struct sk_buff *skb,
 	    neightbl_fill_parms(skb, parms) < 0)
 		goto errout;
 
-	read_unlock_bh(&tbl->lock);
 	nlmsg_end(skb, nlh);
 	return 0;
 errout:
-	read_unlock_bh(&tbl->lock);
 	nlmsg_cancel(skb, nlh);
 	return -EMSGSIZE;
 }
@@ -2575,10 +2565,12 @@ static int neightbl_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
 
 	family = ((struct rtgenmsg *)nlmsg_data(nlh))->rtgen_family;
 
+	rcu_read_lock();
+
 	for (tidx = 0; tidx < NEIGH_NR_TABLES; tidx++) {
 		struct neigh_parms *p;
 
-		tbl = rcu_dereference_rtnl(neigh_tables[tidx]);
+		tbl = rcu_dereference(neigh_tables[tidx]);
 		if (!tbl)
 			continue;
 
@@ -2592,7 +2584,7 @@ static int neightbl_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
 
 		nidx = 0;
 		p = list_next_entry(&tbl->parms, list);
-		list_for_each_entry_from(p, &tbl->parms_list, list) {
+		list_for_each_entry_from_rcu(p, &tbl->parms_list, list) {
 			if (!net_eq(neigh_parms_net(p), net))
 				continue;
 
@@ -2612,6 +2604,8 @@ static int neightbl_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
 		neigh_skip = 0;
 	}
 out:
+	rcu_read_unlock();
+
 	cb->args[0] = tidx;
 	cb->args[1] = nidx;
 
@@ -3913,7 +3907,8 @@ static const struct rtnl_msg_handler neigh_rtnl_msg_handlers[] __initconst = {
 	{.msgtype = RTM_DELNEIGH, .doit = neigh_delete},
 	{.msgtype = RTM_GETNEIGH, .doit = neigh_get, .dumpit = neigh_dump_info,
 	 .flags = RTNL_FLAG_DOIT_UNLOCKED | RTNL_FLAG_DUMP_UNLOCKED},
-	{.msgtype = RTM_GETNEIGHTBL, .dumpit = neightbl_dump_info},
+	{.msgtype = RTM_GETNEIGHTBL, .dumpit = neightbl_dump_info,
+	 .flags = RTNL_FLAG_DUMP_UNLOCKED},
 	{.msgtype = RTM_SETNEIGHTBL, .doit = neightbl_set},
 };