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

[Simon Horman]

On Sat, Aug 15, 2026 at 08:19:32AM +0530, Subasri S wrote:
> 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: syzbot+c06674caba265dc61d46@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=c06674caba265dc61d46
> Fixes: 5bc8e8dbef27 ("netdevsim: add queue management API support")
> Tested-by: syzbot+c06674caba265dc61d46@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Subasri S <subasris1210@xxxxxxxxx>
> ---
> Changes in v2:
> - Restore rxq->napi when reset mode is 1
> - Link to v1: https://lore.kernel.org/r/20260812-net-netdevsim-v1-1-521a85e4fe91@xxxxxxxxx

This appears to be addressing the same issue as:

- [PATCH net] netdevsim: update queue NAPI association on queue reset
  https://lore.kernel.org/netdev/20260817082511.2300402-1-edumazet@xxxxxxxxxx/