linux-kernel - Re: [PATCH v0] idb: Add rtnl

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Date:   Mon, 8 Aug 2022 11:55:11 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Lin Ma <linma@....edu.cn>
Cc:     jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com,
        davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
        ast@...nel.org, daniel@...earbox.net, hawk@...nel.org,
        john.fastabend@...il.com, intel-wired-lan@...ts.osuosl.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH v0] idb: Add rtnl_lock to avoid data race

On Mon,  8 Aug 2022 16:10:50 +0800 Lin Ma wrote:
> The commit c23d92b80e0b ("igb: Teardown SR-IOV before
> unregister_netdev()") places the unregister_netdev() call after the
> igb_disable_sriov() call to avoid functionality issue.
> 
> However, it introduces several race conditions when detaching a device.
> For example, when .remove() is called, the below interleaving leads to
> use-after-free.
> 
>  (FREE from device detaching)      |   (USE from netdev core)
> igb_remove                         |  igb_ndo_get_vf_config
>  igb_disable_sriov                 |  vf >= adapter->vfs_allocated_count?
>   kfree(adapter->vf_data)          |
>   adapter->vfs_allocated_count = 0 |
>                                    |    memcpy(... adapter->vf_data[vf]
> 
> In short, there are data races between read and write of
> adapter->vfs_allocated_count. To fix this, we can add a new lock to
> protect members in adapter object. However, we cau use the existing
> rtnl_lock just as other drivers do. (See how dpaa2_eth_disconnect_mac is
> protected in dpaa2_eth_remove function). This patch adopts similar
> fixes.
> 
> Fixes: c23d92b80e0b ("igb: Teardown SR-IOV before unregister_netdev()")
> Signed-off-by: Lin Ma <linma@....edu.cn>
> ---
>  drivers/net/ethernet/intel/igb/igb_main.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
> index d8b836a85cc3..e86ea4de05f8 100644
> --- a/drivers/net/ethernet/intel/igb/igb_main.c
> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
> @@ -3814,7 +3814,9 @@ static void igb_remove(struct pci_dev *pdev)
>  	igb_release_hw_control(adapter);
>  
>  #ifdef CONFIG_PCI_IOV
> +	rtnl_lock();
>  	igb_disable_sriov(pdev);
> +	rtnl_unlock();
>  #endif
>  
>  	unregister_netdev(netdev);

What about the disable path coming from sysfs? This looks incomplete to
me. Perhaps take a look at commit 1e53834ce541 ("ixgbe: Add locking to
prevent panic when setting sriov_numvfs to zero") for some inspiration.