[PATCH 6.6 015/254] macvlan: fix possible UAF in macvlan_forward_source()

Greg Kroah-Hartman
2026-01-28T15:27:07Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 7470a7a63dc162f07c26dbf960e41ee1e248d80e ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/macvlan.c | 20 +++++++++++++-------
1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
index c8da94af4161a..09db43ce31767 100644
--- a/drivers/net/macvlan.c
+++ b/drivers/net/macvlan.c
@@ -58,7 +58,7 @@ 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;
};
@@ -145,7 +145,7 @@ 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;
@@ -167,7 +167,7 @@ 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++;
@@ -186,6 +186,7 @@ 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);
}
@@ -389,7 +390,7 @@ 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;
@@ -432,9 +433,14 @@ 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);
}
}

@@ -1685,7 +1691,7 @@ 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;
--
2.51.0