[PATCH net 6/6] gve: fix NULL dereference from premature XSK pool DMA unmap

[Joshua Washington <joshwash@google.com>]

To ensure that XSK pools are DMA unmapped in all scenarios, GVE performs
the unmapping before validating if the interface is up and early
returning.

However, if rings are up, this introduces a race between the RX NAPI and
the control plane. As part of DMA unmapping the XSK pool, the kernel
sets pool->dev to NULL. Because xsk_buff_dma_sync_for_cpu() relies on
pool->dev, this results in a kernel panic:

BUG: kernel NULL pointer dereference, address: 000000000000030c
...
RIP: 0010:gve_rx_poll_dqo+0x2e2/0x13b0 [gve]
...
Call Trace:
 <IRQ>
 gve_napi_poll_dqo+0x88/0x170 [gve]
 __napi_poll+0x30/0x210
 net_rx_action+0x210/0x410
 ? dst_destroy_rcu+0x12/0x20
 handle_softirqs+0xe4/0x310
 __irq_exit_rcu+0x10e/0x130
 irq_exit_rcu+0xe/0x20
 common_interrupt+0xb6/0xe0
 </IRQ>

Leave the XSK pool DMA mapped until after rings are guaranteed to no
longer rely on the pool.

Fixes: d57ae093c887 ("gve: deduplicate xdp info and xsk pool registration logic")
Cc: stable@vger.kernel.org
Reviewed-by: Jordan Rhee <jordanrhee@google.com>
Signed-off-by: Joshua Washington <joshwash@google.com>
---
 drivers/net/ethernet/google/gve/gve_main.c | 27 ++++++++++++----------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/drivers/net/ethernet/google/gve/gve_main.c b/drivers/net/ethernet/google/gve/gve_main.c
index e084b367a92d..ccaf5f86a1e6 100644
--- a/drivers/net/ethernet/google/gve/gve_main.c
+++ b/drivers/net/ethernet/google/gve/gve_main.c
@@ -1681,28 +1681,24 @@ static int gve_xsk_pool_disable(struct net_device *dev,
 	struct napi_struct *napi_rx;
 	struct napi_struct *napi_tx;
 	struct xsk_buff_pool *pool;
+	int err = 0;
 	int tx_qid;
-	int err;
 
-	if (qid >= priv->rx_cfg.num_queues)
-		return -EINVAL;
+	if (qid >= priv->rx_cfg.num_queues) {
+		err = -EINVAL;
+		goto unmap_and_return;
+	}
 
 	clear_bit(qid, priv->xsk_pools);
 
-	pool = xsk_get_pool_from_qid(dev, qid);
-	if (pool)
-		xsk_pool_dma_unmap(pool,
-				   DMA_ATTR_SKIP_CPU_SYNC |
-				   DMA_ATTR_WEAK_ORDERING);
-
 	if (!netif_running(dev) || !priv->tx_cfg.num_xdp_queues)
-		return 0;
+		goto unmap_and_return;
 
 	/* Stop and start RDA queues to repost buffers. */
 	if (!gve_is_qpl(priv) && priv->xdp_prog) {
 		err = gve_configure_rings_xdp(priv, priv->rx_cfg.num_queues);
 		if (err)
-			return err;
+			goto unmap_and_return;
 	}
 
 	napi_rx = &priv->ntfy_blocks[priv->rx[qid].ntfy_id].napi;
@@ -1725,7 +1721,14 @@ static int gve_xsk_pool_disable(struct net_device *dev,
 			napi_schedule(napi_tx);
 	}
 
-	return 0;
+unmap_and_return:
+	pool = xsk_get_pool_from_qid(dev, qid);
+	if (pool)
+		xsk_pool_dma_unmap(pool,
+				   DMA_ATTR_SKIP_CPU_SYNC |
+				   DMA_ATTR_WEAK_ORDERING);
+
+	return err;
 }
 
 static int gve_xsk_wakeup(struct net_device *dev, u32 queue_id, u32 flags)
-- 
2.55.0.691.gc56d675ccc-goog