veth: fix NAPI leak in XDP enable error path

[ Upstream commit 6739027 ]

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: b02e5a0 ("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>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Link: https://patch.msgid.link/20260622111825.88337-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: edumazet

drivers/net/veth.c

@@ -1082,6 +1082,8 @@ 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];