[PATCH net] veth: manage XDP program pointers during channel resize

[Weiming Shi <bestswngs@gmail.com>]

veth_set_channels() tears down XDP resources for removed RX queues
without clearing rq->xdp_prog.  If the program is then detached or
replaced, those queues keep the old pointer after bpf_prog_put().  A
later channel increase can re-enable NAPI and run the freed program.

Clear the program pointer after taking an RX queue offline, and publish
the current program only after bringing the queue back online succeeds.

  BUG: unable to handle page fault for address: ffffc90000256048
  Oops: Oops: 0000 [#1] SMP KASAN NOPTI
  RIP: veth_xdp_rcv_skb (include/linux/filter.h:779
                         include/net/xdp.h:696 drivers/net/veth.c:820)
  Call Trace:
   veth_xdp_rcv (drivers/net/veth.c:941)
   veth_poll (drivers/net/veth.c:986)
   __napi_poll (net/core/dev.c:7787)
   net_rx_action (net/core/dev.c:7850 net/core/dev.c:8007)
   handle_softirqs (kernel/softirq.c:645)
  Kernel panic - not syncing: Fatal exception in interrupt

Cc: stable@vger.kernel.org
Fixes: 4752eeb3d891 ("veth: implement support for set_channel ethtool op")
Reported-by: <co+65e5c76b187f08b2@bugs.sh>
Assisted-by: LLM
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
---
 drivers/net/veth.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 6ed3ee81153fb..ef7624bc2c0ec 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -1247,12 +1247,15 @@ static int veth_napi_enable(struct net_device *dev)
 static void veth_disable_range_safe(struct net_device *dev, int start, int end)
 {
 	struct veth_priv *priv = netdev_priv(dev);
+	int i;
 
 	if (start >= end)
 		return;
 
 	if (priv->_xdp_prog) {
 		veth_napi_del_range(dev, start, end);
+		for (i = start; i < end; i++)
+			rcu_assign_pointer(priv->rq[i].xdp_prog, NULL);
 		veth_disable_xdp_range(dev, start, end, false);
 	} else if (veth_gro_requested(dev)) {
 		veth_napi_del_range(dev, start, end);
@@ -1262,7 +1265,7 @@ static void veth_disable_range_safe(struct net_device *dev, int start, int end)
 static int veth_enable_range_safe(struct net_device *dev, int start, int end)
 {
 	struct veth_priv *priv = netdev_priv(dev);
-	int err;
+	int err, i;
 
 	if (start >= end)
 		return 0;
@@ -1281,6 +1284,9 @@ static int veth_enable_range_safe(struct net_device *dev, int start, int end)
 			veth_disable_xdp_range(dev, start, end, true);
 			return err;
 		}
+		for (i = start; i < end; i++)
+			rcu_assign_pointer(priv->rq[i].xdp_prog,
+					   priv->_xdp_prog);
 	} else if (veth_gro_requested(dev)) {
 		return veth_napi_enable_range(dev, start, end);
 	}
-- 
2.55.0