netdev - [PATCH net 2/8] ndisc: use RCU protection in ndisc_alloc

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Message-ID: <20250207135841.1948589-3-edumazet@google.com>
Date: Fri,  7 Feb 2025 13:58:34 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, David Ahern <dsahern@...nel.org>, 
	Kuniyuki Iwashima <kuniyu@...zon.com>, Simon Horman <horms@...nel.org>, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net 2/8] ndisc: use RCU protection in ndisc_alloc_skb()

ndisc_alloc_skb() can be called without RTNL or RCU being held.

Add RCU protection to avoid possible UAF.

Fixes: de09334b9326 ("ndisc: Introduce ndisc_alloc_skb() helper.")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv6/ndisc.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 264b10a94757705d4ce61e1371eb4d9a699b9016..90f8aa2d7af2ec1103220378c155b7b724efc575 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -418,15 +418,11 @@ static struct sk_buff *ndisc_alloc_skb(struct net_device *dev,
 {
 	int hlen = LL_RESERVED_SPACE(dev);
 	int tlen = dev->needed_tailroom;
-	struct sock *sk = dev_net(dev)->ipv6.ndisc_sk;
 	struct sk_buff *skb;
 
 	skb = alloc_skb(hlen + sizeof(struct ipv6hdr) + len + tlen, GFP_ATOMIC);
-	if (!skb) {
-		ND_PRINTK(0, err, "ndisc: %s failed to allocate an skb\n",
-			  __func__);
+	if (!skb)
 		return NULL;
-	}
 
 	skb->protocol = htons(ETH_P_IPV6);
 	skb->dev = dev;
@@ -437,7 +433,9 @@ static struct sk_buff *ndisc_alloc_skb(struct net_device *dev,
 	/* Manually assign socket ownership as we avoid calling
 	 * sock_alloc_send_pskb() to bypass wmem buffer limits
 	 */
-	skb_set_owner_w(skb, sk);
+	rcu_read_lock();
+	skb_set_owner_w(skb, dev_net_rcu(dev)->ipv6.ndisc_sk);
+	rcu_read_unlock();
 
 	return skb;
 }
-- 
2.48.1.502.g6dc24dfdaf-goog