linux-kernel - Re: [PATCH] net: core: Fix possible null-pointer dereference in failover_slave

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Date:   Tue, 10 Aug 2021 08:04:04 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Tuo Li <islituo@...il.com>
Cc:     sridhar.samudrala@...el.com, davem@...emloft.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        baijiaju1990@...il.com, TOTE Robot <oslab@...nghua.edu.cn>
Subject: Re: [PATCH] net: core: Fix possible null-pointer dereference in
 failover_slave_register()

On Tue, 10 Aug 2021 02:18:00 -0700 Tuo Li wrote:
> The variable fops is checked in:
>   if (fops && fops->slave_pre_register &&
>     fops->slave_pre_register(slave_dev, failover_dev))
> 
> This indicates that it can be NULL.
> However, it is dereferenced when calling netdev_rx_handler_register():
>   err = netdev_rx_handler_register(slave_dev, fops->slave_handle_frame,
>                     failover_dev);
> 
> To fix this possible null-pointer dereference, check fops first, and if 
> it is NULL, assign -EINVAL to err.

The other fops checks look like defensive programming. I don't see
anywhere where fops would be cleared, and all callers pass it to
register().