netdev - Re: [net] net-sysfs: avoid registering new queue objects after device unregistration

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Message-Id: <20211026.153057.208749798584527471.davem@davemloft.net>
Date:   Tue, 26 Oct 2021 15:30:57 +0100 (BST)
From:   David Miller <davem@...emloft.net>
To:     atenart@...nel.org
Cc:     kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org
Subject: Re: [net] net-sysfs: avoid registering new queue objects after
 device unregistration

From: Antoine Tenart <atenart@...nel.org>
Date: Tue, 26 Oct 2021 15:38:22 +0200

> netdev_queue_update_kobjects can be called after device unregistration
> started (and device_del was called) resulting in two issues: possible
> registration of new queue kobjects (leading to the following trace) and
> providing a wrong 'old_num' number (because real_num_tx_queues is not
> updated in the unregistration path).
> 
>   BUG: KASAN: use-after-free in kobject_get+0x14/0x90
>   Read of size 1 at addr ffff88801961248c by task ethtool/755
> 
>   CPU: 0 PID: 755 Comm: ethtool Not tainted 5.15.0-rc6+ #778
>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/014
>   Call Trace:
>    dump_stack_lvl+0x57/0x72
>    print_address_description.constprop.0+0x1f/0x140
>    kasan_report.cold+0x7f/0x11b
>    kobject_get+0x14/0x90
>    kobject_add_internal+0x3d1/0x450
>    kobject_init_and_add+0xba/0xf0
>    netdev_queue_update_kobjects+0xcf/0x200
>    netif_set_real_num_tx_queues+0xb4/0x310
>    veth_set_channels+0x1c3/0x550
>    ethnl_set_channels+0x524/0x610
> 
> The fix for both is to only allow unregistering queue kobjects after a
> net device started its unregistration and to ensure we know the current
> Tx queue number (we update dev->real_num_tx_queues before returning).
> This relies on the fact that dev->real_num_tx_queues is used for
> 'old_num' expect when firstly allocating queues.
> 
> (Rx queues are not affected as net_rx_queue_update_kobjects can't be
> called after a net device started its unregistration).
> 
> Fixes: 5c56580b74e5 ("net: Adjust TX queue kobjects if number of queues changes during unregister")
> Signed-off-by: Antoine Tenart <atenart@...nel.org>

netdev_queue_update_kobjects is a confusing function name, it sounds like it handles both rx and tx.
It only handles tx so net_tx_queue_update_kobjects is more appropriate.

Could you rename the function in this patch please?

Thank you.