[PATCH v2] netdevsim: update rxq->napi pointer during queue reset

In netdevsim, when queue reset is performed using debugfs, it triggers
these sequence of operations: nsim_queue_stop() -> nsim_queue_start()
-> nsim_queue_mem_free(). nsim_queue_mem_free() frees the old
nsim_rq struct which embeds the napi_struct. But the rxq->napi pointer
in the struct netdev_rx_queue still points to the old nsim_rq's embedded
napi_struct. So, any subsequent xsk_bind() which reads rxq->napi->napi_id
after a queue reset is a use-after-free.

Add netif_queue_set_napi() calls to nsim_queue_stop() and
nsim_queue_start() which clears the rxq->napi during stop
and sets it to the new napi instance during start.

KASAN report:

Call Trace:
 kasan_report+0xdf/0x1c0 mm/kasan/report.c:595
 xsk_bind+0x1582/0x16c0 net/xdp/xsk.c:1758
 __sys_bind_socket net/socket.c:1920 [inline]
 __sys_bind_socket net/socket.c:1912 [inline]
 __sys_bind+0x1a9/0x260 net/socket.c:1951

Allocated by task 5622:
 nsim_queue_alloc+0x3c/0x140 drivers/net/netdevsim/netdev.c:715
 nsim_queue_init drivers/net/netdevsim/netdev.c:1012 [inline]
 nsim_init_netdevsim drivers/net/netdevsim/netdev.c:1059 [inline]
 nsim_create+0xb13/0x1420 drivers/net/netdevsim/netdev.c:1152
 __nsim_dev_port_add+0x3ba/0x8f0 drivers/net/netdevsim/dev.c:1509
 nsim_dev_port_add_all drivers/net/netdevsim/dev.c:1570 [inline]
 nsim_drv_probe+0xdbd/0x13a0 drivers/net/netdevsim/dev.c:1731

Freed by task 5659:
 slab_free mm/slub.c:6377 [inline]
 kfree+0x22b/0x6c0 mm/slub.c:6692
 nsim_queue_mem_free+0xfe/0x190 drivers/net/netdevsim/netdev.c:796
 netdev_rx_queue_reconfig+0x405/0x630 net/core/netdev_rx_queue.c:144
 netdev_rx_queue_restart+0x8f/0xc0 net/core/netdev_rx_queue.c:183
 nsim_qreset_write+0x2e3/0x410 drivers/net/netdevsim/netdev.c:887

Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=c06674caba265dc61d46
Fixes: 5bc8e8dbef27 ("netdevsim: add queue management API support")
Tested-by: [email protected]
Signed-off-by: Subasri S <[email protected]>
---
Changes in v2:
- Restore rxq->napi when reset mode is 1
- Link to v1: https://lore.kernel.org/r/[email protected]
---
 drivers/net/netdevsim/netdev.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index 4e9d7e10b527..291d34718b2e 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c
@@ -808,6 +808,8 @@ nsim_queue_start(struct net_device *dev, struct netdev_queue_config *qcfg,
 
 	if (ns->rq_reset_mode == 1) {
 		ns->rq[idx]->page_pool = qmem->pp;
+		netif_queue_set_napi(dev, idx, NETDEV_QUEUE_TYPE_RX,
+				     &ns->rq[idx]->napi);
 		napi_enable_locked(&ns->rq[idx]->napi);
 		return 0;
 	}
@@ -826,6 +828,8 @@ nsim_queue_start(struct net_device *dev, struct netdev_queue_config *qcfg,
 	}
 
 	ns->rq[idx] = qmem->rq;
+	netif_queue_set_napi(dev, idx, NETDEV_QUEUE_TYPE_RX,
+			     &ns->rq[idx]->napi);
 	napi_enable_locked(&ns->rq[idx]->napi);
 
 	return 0;
@@ -838,6 +842,7 @@ static int nsim_queue_stop(struct net_device *dev, void *per_queue_mem, int idx)
 
 	netdev_assert_locked(dev);
 
+	netif_queue_set_napi(dev, idx, NETDEV_QUEUE_TYPE_RX, NULL);
 	napi_disable_locked(&ns->rq[idx]->napi);
 
 	if (ns->rq_reset_mode == 1) {

---
base-commit: a59f57e2aa127c5354168d2ec4bac920df1be4f4
change-id: 20260812-net-netdevsim-aad6100834dd

Best regards,
-- 
Subasri S <[email protected]>