On Thu, Aug 27, 2026 at 04:29:28PM +0200, Florian Westphal wrote:
> co <[email protected]> wrote:
> > We found a bug reachable in:
> >
> > path net/bridge/netfilter
> > crash out-of-bounds in br_forward()
> > commit 7b5344954050 ("Merge tag 'nf-26-08-10' of
> > git://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf")
>
> I'm looking into these reports, I think this is the same
> underlying bug as the other report; a variant of
>
> ccb9fd4b8753 ("netfilter: revalidate bridge ports")
>
> That bug uses nfnetlink_queue for RCU escape, the other two reports
> use defrag engine.
I started this patch. I think this can still happen with native
nfnetlink_queue support for the bridge family?
diff --git a/net/bridge/netfilter/nft_reject_bridge.c
b/net/bridge/netfilter/nft_reject_bridge.c
index cd2b04236a99..b3a51ba72e9c 100644
--- a/net/bridge/netfilter/nft_reject_bridge.c
+++ b/net/bridge/netfilter/nft_reject_bridge.c
@@ -44,7 +44,7 @@ static void nft_reject_br_push_etherhdr(struct sk_buff
*oldskb,
*/
static void nft_reject_br_send_v4_tcp_reset(struct net *net,
struct sk_buff *oldskb,
- const struct net_device *dev,
+ struct net_bridge_port *port,
int hook)
{
struct sk_buff *nskb;
@@ -55,12 +55,12 @@ static void nft_reject_br_send_v4_tcp_reset(struct net *net,
nft_reject_br_push_etherhdr(oldskb, nskb);
- br_forward(br_port_get_rcu(dev), nskb, false, true);
+ br_forward(port, nskb, false, true);
}
static void nft_reject_br_send_v4_unreach(struct net *net,
struct sk_buff *oldskb,
- const struct net_device *dev,
+ struct net_bridge_port *port,
int hook, u8 code)
{
struct sk_buff *nskb;
@@ -71,12 +71,12 @@ static void nft_reject_br_send_v4_unreach(struct net *net,
nft_reject_br_push_etherhdr(oldskb, nskb);
- br_forward(br_port_get_rcu(dev), nskb, false, true);
+ br_forward(port, nskb, false, true);
}
static void nft_reject_br_send_v6_tcp_reset(struct net *net,
struct sk_buff *oldskb,
- const struct net_device *dev,
+ struct net_bridge_port *port,
int hook)
{
struct sk_buff *nskb;
@@ -87,13 +87,13 @@ static void nft_reject_br_send_v6_tcp_reset(struct net *net,
nft_reject_br_push_etherhdr(oldskb, nskb);
- br_forward(br_port_get_rcu(dev), nskb, false, true);
+ br_forward(port, nskb, false, true);
}
static void nft_reject_br_send_v6_unreach(struct net *net,
struct sk_buff *oldskb,
- const struct net_device *dev,
+ struct net_bridge_port *port,
int hook, u8 code)
{
struct sk_buff *nskb;
@@ -104,37 +104,47 @@ static void nft_reject_br_send_v6_unreach(struct net *net,
nft_reject_br_push_etherhdr(oldskb, nskb);
- br_forward(br_port_get_rcu(dev), nskb, false, true);
+ br_forward(port, nskb, false, true);
}
static void nft_reject_bridge_eval(const struct nft_expr *expr,
struct nft_regs *regs,
const struct nft_pktinfo *pkt)
{
- struct nft_reject *priv = nft_expr_priv(expr);
const unsigned char *dest = eth_hdr(pkt->skb)->h_dest;
+ struct nft_reject *priv = nft_expr_priv(expr);
+ const struct net_device *dev = nft_in(pkt);
+ struct net_bridge_port *port;
if (is_broadcast_ether_addr(dest) ||
is_multicast_ether_addr(dest))
goto out;
+ if (!dev || !netif_is_bridge_port(dev) ||
+ netdev_master_upper_dev_get_rcu((struct net_device *)dev))
+ goto out;
+
+ port = br_port_get_rcu(dev);
+ if (!port)
+ goto out;
+
switch (eth_hdr(pkt->skb)->h_proto) {
case htons(ETH_P_IP):
switch (priv->type) {
case NFT_REJECT_ICMP_UNREACH:
nft_reject_br_send_v4_unreach(nft_net(pkt), pkt->skb,
- nft_in(pkt),
+ port,
nft_hook(pkt),
priv->icmp_code);
break;
case NFT_REJECT_TCP_RST:
nft_reject_br_send_v4_tcp_reset(nft_net(pkt), pkt->skb,
- nft_in(pkt),
+ port,
nft_hook(pkt));
break;
case NFT_REJECT_ICMPX_UNREACH:
nft_reject_br_send_v4_unreach(nft_net(pkt), pkt->skb,
- nft_in(pkt),
+ port,
nft_hook(pkt),
nft_reject_icmp_code(priv->icmp_code));
break;
@@ -144,18 +154,18 @@ static void nft_reject_bridge_eval(const struct nft_expr
*expr,
switch (priv->type) {
case NFT_REJECT_ICMP_UNREACH:
nft_reject_br_send_v6_unreach(nft_net(pkt), pkt->skb,
- nft_in(pkt),
+ port,
nft_hook(pkt),
priv->icmp_code);
break;
case NFT_REJECT_TCP_RST:
nft_reject_br_send_v6_tcp_reset(nft_net(pkt), pkt->skb,
- nft_in(pkt),
+ port,
nft_hook(pkt));
break;
case NFT_REJECT_ICMPX_UNREACH:
nft_reject_br_send_v6_unreach(nft_net(pkt), pkt->skb,
- nft_in(pkt),
+ port,
nft_hook(pkt),
nft_reject_icmpv6_code(priv->icmp_code));
break;
