netdev - Re: [PATCH 4.9.y] net: sched: prevent UAF on tc_ctl_tfilter when temporarily dropping rtnl

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Message-ID: <YnEy2726cz98I6YC@kroah.com>
Date:   Tue, 3 May 2022 15:49:15 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Cc:     stable@...r.kernel.org, netdev@...r.kernel.org, kuba@...nel.org,
        davem@...emloft.net, jiri@...nulli.us, xiyou.wangcong@...il.com,
        jhs@...atatu.com, vladbu@...lanox.com
Subject: Re: [PATCH 4.9.y] net: sched: prevent UAF on tc_ctl_tfilter when
 temporarily dropping rtnl_lock

On Mon, May 02, 2022 at 05:49:24PM -0300, Thadeu Lima de Souza Cascardo wrote:
> When dropping the rtnl_lock for looking up for a module, the device may be
> removed, releasing the qdisc and class memory. Right after trying to load
> the module, cl_ops->put is called, leading to a potential use-after-free.
> 
> Though commit e368fdb61d8e ("net: sched: use Qdisc rcu API instead of
> relying on rtnl lock") fixes this, it involves a lot of refactoring of the
> net/sched/ code, complicating its backport.

What about 4.14.y?  We can not take a commit for 4.9.y with it also
being broken in 4.14.y, and yet fixed in 4.19.y, right?  Anyone who
updates from 4.9 to 4.14 will have a regression.

thanks,

greg k-h