[PATCH net] veth: fix NAPI leak in XDP enable error path

[Eric Dumazet <edumazet@google.com>]

During XDP enablement in veth, if xdp_rxq_info_reg() or
xdp_rxq_info_reg_mem_model() fails, the driver rolls back the changes.

However, the rollback loop:
	for (i--; i >= start; i--) {

decrements the loop index 'i' before the first iteration. This
correctly skips unregistering the rxq for the failed index 'i' (as
registration failed or was already cleaned up), but it also
erroneously skips calling netif_napi_deli() for rq[i].xdp_napi.

Since netif_napi_add() was already called for index 'i', this leaves
a dangling napi_struct in the device's napi_list. When the veth
device is later destroyed, the freed queue memory (which contains the
leaked NAPI structure) can be reused.

The subsequent device teardown iterates the NAPI list and
corrupts the reallocated memory, leading to UAF.

Fix this by explicitly deleting the NAPI association for the failed
index 'i' before rolling back the successfully configured queues.

Fixes: b02e5a0ebb17 ("xsk: Propagate napi_id to XDP socket Rx path")
Reported-by: Guenter Roeck <groeck@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Björn Töpel <bjorn.topel@intel.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Tariq Toukan <tariqt@nvidia.com>
---
 drivers/net/veth.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 0cfb19b760dd54eb896f469c02bb02ecf5eef504..1c5142149175369a642342849addfbb9c07404bc 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -1137,6 +1137,8 @@ static int veth_enable_xdp_range(struct net_device *dev, int start, int end,
 err_reg_mem:
 	xdp_rxq_info_unreg(&priv->rq[i].xdp_rxq);
 err_rxq_reg:
+	if (!napi_already_on)
+		netif_napi_del(&priv->rq[i].xdp_napi);
 	for (i--; i >= start; i--) {
 		struct veth_rq *rq = &priv->rq[i];
 
-- 
2.55.0.rc0.786.g65d90a0328-goog