macvlan: fix possible UAF in macvlan_forward_source()

Add RCU protection on (struct macvlan_source_entry)->vlan.

Whenever macvlan_hash_del_source() is called, we must clear
entry->vlan pointer before RCU grace period starts.

This allows macvlan_forward_source() to skip over
entries queued for freeing.

Note that macvlan_dev are already RCU protected, as they
are embedded in a standard netdev (netdev_priv(ndev)).

Fixes: 79cf79abce71 ("macvlan: add source mode")
Reported-by: syzbot+7182fbe91e58602ec1fe@syzkaller.appspotmail.com
https: //lore.kernel.org/netdev/695fb1e8.050a0220.1c677c.039f.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260108133651.1130486-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index 7966545512cfeab3914374675bafa3847e5d7ae1..b4df7e184791d0fe0a60c17522b91b2766847b37 100644 (file)
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -59,7 +59,7 @@ struct macvlan_port {
 
 struct macvlan_source_entry {
        struct hlist_node       hlist;
-       struct macvlan_dev      *vlan;
+       struct macvlan_dev __rcu *vlan;
        unsigned char           addr[6+2] __aligned(sizeof(u16));
        struct rcu_head         rcu;
 };
@@ -146,7 +146,7 @@ static struct macvlan_source_entry *macvlan_hash_lookup_source(
 
        hlist_for_each_entry_rcu(entry, h, hlist, lockdep_rtnl_is_held()) {
                if (ether_addr_equal_64bits(entry->addr, addr) &&
-                   entry->vlan == vlan)
+                   rcu_access_pointer(entry->vlan) == vlan)
                        return entry;
        }
        return NULL;
@@ -168,7 +168,7 @@ static int macvlan_hash_add_source(struct macvlan_dev *vlan,
                return -ENOMEM;
 
        ether_addr_copy(entry->addr, addr);
-       entry->vlan = vlan;
+       RCU_INIT_POINTER(entry->vlan, vlan);
        h = &port->vlan_source_hash[macvlan_eth_hash(addr)];
        hlist_add_head_rcu(&entry->hlist, h);
        vlan->macaddr_count++;
@@ -187,6 +187,7 @@ static void macvlan_hash_add(struct macvlan_dev *vlan)
 
 static void macvlan_hash_del_source(struct macvlan_source_entry *entry)
 {
+       RCU_INIT_POINTER(entry->vlan, NULL);
        hlist_del_rcu(&entry->hlist);
        kfree_rcu(entry, rcu);
 }
@@ -390,7 +391,7 @@ static void macvlan_flush_sources(struct macvlan_port *port,
        int i;
 
        hash_for_each_safe(port->vlan_source_hash, i, next, entry, hlist)
-               if (entry->vlan == vlan)
+               if (rcu_access_pointer(entry->vlan) == vlan)
                        macvlan_hash_del_source(entry);
 
        vlan->macaddr_count = 0;
@@ -433,9 +434,14 @@ static bool macvlan_forward_source(struct sk_buff *skb,
 
        hlist_for_each_entry_rcu(entry, h, hlist) {
                if (ether_addr_equal_64bits(entry->addr, addr)) {
-                       if (entry->vlan->flags & MACVLAN_FLAG_NODST)
+                       struct macvlan_dev *vlan = rcu_dereference(entry->vlan);
+
+                       if (!vlan)
+                               continue;
+
+                       if (vlan->flags & MACVLAN_FLAG_NODST)
                                consume = true;
-                       macvlan_forward_source_one(skb, entry->vlan);
+                       macvlan_forward_source_one(skb, vlan);
                }
        }
 
@@ -1680,7 +1686,7 @@ static int macvlan_fill_info_macaddr(struct sk_buff *skb,
        struct macvlan_source_entry *entry;
 
        hlist_for_each_entry_rcu(entry, h, hlist, lockdep_rtnl_is_held()) {
-               if (entry->vlan != vlan)
+               if (rcu_access_pointer(entry->vlan) != vlan)
                        continue;
                if (nla_put(skb, IFLA_MACVLAN_MACADDR, ETH_ALEN, entry->addr))
                        return 1;