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@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250207135841.1948589-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 264b10a94757705d4ce61e1371eb4d9a699b9016..90f8aa2d7af2ec1103220378c155b7b724efc575 100644 (file)
--- 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;
 }