netdev - [PATCH v1 net-next 4/7] neighbour: Move neigh_find_table() to neigh

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Message-ID: <20250416004253.20103-5-kuniyu@amazon.com>
Date: Tue, 15 Apr 2025 17:41:27 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>
CC: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...zon.com>,
	Kuniyuki Iwashima <kuni1840@...il.com>, <netdev@...r.kernel.org>
Subject: [PATCH v1 net-next 4/7] neighbour: Move neigh_find_table() to neigh_get().

neigh_valid_get_req() calls neigh_find_table() to fetch neigh_tables[].

neigh_find_table() uses rcu_dereference_rtnl(), but RTNL actually does
not protect it at all; neigh_table_clear() can be called without RTNL
and only waits for RCU readers by synchronize_rcu().

Fortunately, there is no bug because IPv4 is built-in, IPv6 cannot be
unloaded, and DECNET was removed.

To fetch neigh_tables[] by rcu_dereference() later, let's move
neigh_find_table() from neigh_valid_get_req() to neigh_get().

Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
 net/core/neighbour.c | 38 ++++++++++++++++++++------------------
 1 file changed, 20 insertions(+), 18 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 297954ff13a8..58a6821dae3d 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -2847,10 +2847,9 @@ static int neigh_dump_info(struct sk_buff *skb, struct netlink_callback *cb)
 }
 
 static struct ndmsg *neigh_valid_get_req(const struct nlmsghdr *nlh,
-					 struct neigh_table **tbl, void **dst,
+					 struct nlattr **tb,
 					 struct netlink_ext_ack *extack)
 {
-	struct nlattr *tb[NDA_MAX + 1];
 	struct ndmsg *ndm;
 	int err = -EINVAL;
 	int i;
@@ -2882,13 +2881,6 @@ static struct ndmsg *neigh_valid_get_req(const struct nlmsghdr *nlh,
 	if (err < 0)
 		goto err;
 
-	*tbl = neigh_find_table(ndm->ndm_family);
-	if (!*tbl) {
-		NL_SET_ERR_MSG(extack, "Unsupported family in header for neighbor get request");
-		err = -EAFNOSUPPORT;
-		goto err;
-	}
-
 	for (i = 0; i <= NDA_MAX; ++i) {
 		switch (i) {
 		case NDA_DST:
@@ -2896,12 +2888,6 @@ static struct ndmsg *neigh_valid_get_req(const struct nlmsghdr *nlh,
 				NL_SET_ERR_MSG(extack, "Network address not specified");
 				goto err;
 			}
-
-			if (nla_len(tb[i]) != (int)(*tbl)->key_len) {
-				NL_SET_ERR_MSG(extack, "Invalid network address in neighbor get request");
-				goto err;
-			}
-			*dst = nla_data(tb[i]);
 			break;
 		default:
 			if (!tb[i])
@@ -2941,16 +2927,17 @@ static int neigh_get(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 {
 	struct net *net = sock_net(in_skb->sk);
 	u32 pid = NETLINK_CB(in_skb).portid;
+	struct nlattr *tb[NDA_MAX + 1];
 	struct net_device *dev = NULL;
-	struct neigh_table *tbl = NULL;
 	u32 seq = nlh->nlmsg_seq;
+	struct neigh_table *tbl;
 	struct neighbour *neigh;
 	struct sk_buff *skb;
 	struct ndmsg *ndm;
-	void *dst = NULL;
+	void *dst;
 	int err;
 
-	ndm = neigh_valid_get_req(nlh, &tbl, &dst, extack);
+	ndm = neigh_valid_get_req(nlh, tb, extack);
 	if (IS_ERR(ndm))
 		return PTR_ERR(ndm);
 
@@ -2961,6 +2948,21 @@ static int neigh_get(struct sk_buff *in_skb, struct nlmsghdr *nlh,
 	if (!skb)
 		return -ENOBUFS;
 
+	tbl = neigh_find_table(ndm->ndm_family);
+	if (!tbl) {
+		NL_SET_ERR_MSG(extack, "Unsupported family in header for neighbor get request");
+		err = -EAFNOSUPPORT;
+		goto err;
+	}
+
+	if (nla_len(tb[NDA_DST]) != (int)tbl->key_len) {
+		NL_SET_ERR_MSG(extack, "Invalid network address in neighbor get request");
+		err = -EINVAL;
+		goto err;
+	}
+
+	dst = nla_data(tb[NDA_DST]);
+
 	if (ndm->ndm_ifindex) {
 		dev = __dev_get_by_index(net, ndm->ndm_ifindex);
 		if (!dev) {
-- 
2.49.0