[PATCH 4.19 04/96] net: bridge: fix per-port af_packet sockets

Greg Kroah-Hartman
2019-04-24T17:30:52Z

From: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>

[ Upstream commit 3b2e2904deb314cc77a2192f506f2fd44e3d10d0 ]

When the commit below was introduced it changed two visible things:
- the skb was no longer passed through the protocol handlers with the
original device
- the skb was passed up the stack with skb->dev = bridge

The first change broke af_packet sockets on bridge ports. For example we
use them for hostapd which listens for ETH_P_PAE packets on the ports.
We discussed two possible fixes:
- create a clone and pass it through NF_HOOK(), act on the original skb
based on the result
- somehow signal to the caller from the okfn() that it was called,
meaning the skb is ok to be passed, which this patch is trying to
implement via returning 1 from the bridge link-local okfn()

Note that we rely on the fact that NF_QUEUE/STOLEN would return 0 and
drop/error would return < 0 thus the okfn() is called only when the
return was 1, so we signal to the caller that it was called by preserving
the return value from nf_hook().

Fixes: 8626c56c8279 ("bridge: fix potential use-after-free when hook returns QUEUE or STOLEN verdict")
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/bridge/br_input.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)

--- a/net/bridge/br_input.c
+++ b/net/bridge/br_input.c
@@ -195,13 +195,10 @@ static void __br_handle_local_finish(str
/* note: already called with rcu_read_lock */
static int br_handle_local_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
{
- struct net_bridge_port *p = br_port_get_rcu(skb->dev);
-
__br_handle_local_finish(skb);

- BR_INPUT_SKB_CB(skb)->brdev = p->br->dev;
- br_pass_frame_up(skb);
- return 0;
+ /* return 1 to signal the okfn() was called so it's ok to use the skb */
+ return 1;
}

/*
@@ -278,10 +275,18 @@ rx_handler_result_t br_handle_frame(stru
goto forward;
}

- /* Deliver packet to local host only */
- NF_HOOK(NFPROTO_BRIDGE, NF_BR_LOCAL_IN, dev_net(skb->dev),
- NULL, skb, skb->dev, NULL, br_handle_local_finish);
- return RX_HANDLER_CONSUMED;
+ /* The else clause should be hit when nf_hook():
+ * - returns < 0 (drop/error)
+ * - returns = 0 (stolen/nf_queue)
+ * Thus return 1 from the okfn() to signal the skb is ok to pass
+ */
+ if (NF_HOOK(NFPROTO_BRIDGE, NF_BR_LOCAL_IN,
+ dev_net(skb->dev), NULL, skb, skb->dev, NULL,
+ br_handle_local_finish) == 1) {
+ return RX_HANDLER_PASS;
+ } else {
+ return RX_HANDLER_CONSUMED;
+ }
}