Re: [PATCH net 1/2] net: cpsw: unregister secondary netdev on probe failure

[netdev-bot+sashiko@kernel.org]

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- [High] In this patch, the cpsw_probe() error label
  clean_unregister_netdev_ret in drivers/net/ethernet/ti/cpsw.c now…

--

net: cpsw: unregister secondary netdev on probe failure

This patch records whether cpsw_probe() registered the secondary
dual-EMAC netdev. If it did, the clean_unregister_netdev_ret error path
now unregisters it before the primary netdev. This avoids the reg_state
BUG_ON in free_netdev() when devres frees a netdev that is still
registered after a late IRQ request failure.

> diff --git a/drivers/net/ethernet/ti/cpsw.c b/drivers/net/ethernet/ti/cpsw.c
> index aa3531e844e87..4fc59f9f23fcb 100644
> --- a/drivers/net/ethernet/ti/cpsw.c
> +++ b/drivers/net/ethernet/ti/cpsw.c

[ ... ]

> @@ -1764,6 +1766,8 @@ static int cpsw_probe(struct platform_device *pdev)
>  	return 0;
>  
>  clean_unregister_netdev_ret:
> +	if (secondary_registered)
> +		unregister_netdev(cpsw->slaves[1].ndev);
>  	unregister_netdev(ndev);

[Severity: High]
Can rx_mode_work still be pending on either netdev when devres frees it?

Both netdevs are registered before the devm_request_irq() calls, so an
interface can be brought up during that window. Bringing it up, or
changing its address lists, reaches cpsw_ndo_set_rx_mode(), which does:

    schedule_work(&priv->rx_mode_work);

cpsw_ndo_stop() does not cancel this work.

cpsw_remove() follows each unregister with a disable:

    priv = netdev_priv(ndev);
    unregister_netdev(ndev);
    disable_work_sync(&priv->rx_mode_work);

This error path does not. After probe returns the error, devres calls
free_netdev() on the devm-allocated netdevs. A queued or rtnl-blocked
cpsw_ndo_set_rx_mode_work() would then dereference the freed priv,
priv->cpsw and priv->ndev. The workqueue core would also touch the freed
work_struct.

The primary netdev already had this gap. For the secondary netdev, the
free_netdev() BUG_ON used to fire first. This patch removes that BUG_ON,
so the use-after-free on the secondary netdev can now be reached.

The next patch in the series, "net: cpsw: cancel RX mode work on probe
failure", appears to fix this. It adds disable_work_sync() after both
unregister_netdev() calls here, which matches cpsw_remove(). Its commit
message quotes a KASAN report of "slab-use-after-free in
cpsw_ndo_set_rx_mode_work".

Could that change be folded into this patch, so the two are not applied
separately?

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/cover.1791035789.git.kmehltretter%40gmail.com