netdev - Re: [PATCH net] net/tls: Remove the context from the list in tls_device

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Date:   Mon, 25 Jul 2022 14:35:08 +0000
From:   Maxim Mikityanskiy <maximmi@...dia.com>
To:     "kuba@...nel.org" <kuba@...nel.org>
CC:     Tariq Toukan <tariqt@...dia.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Boris Pismenny <borisp@...dia.com>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [PATCH net] net/tls: Remove the context from the list in
 tls_device_down

On Fri, 2022-07-22 at 15:04 -0700, Jakub Kicinski wrote:
> On Thu, 21 Jul 2022 12:11:27 +0300 Maxim Mikityanskiy wrote:
> > tls_device_down takes a reference on all contexts it's going to move to
> > the degraded state (software fallback). If sk_destruct runs afterwards,
> > it can reduce the reference counter back to 1 and return early without
> > destroying the context. Then tls_device_down will release the reference
> > it took and call tls_device_free_ctx. However, the context will still
> > stay in tls_device_down_list forever. The list will contain an item,
> > memory for which is released, making a memory corruption possible.
> > 
> > Fix the above bug by properly removing the context from all lists before
> > any call to tls_device_free_ctx.
> 
> SGTM. The tls_device_down_list has no use, tho, is the plan to remove
> it later as a cleanup or your upcoming patches make use of it?

I don't plan to remove it. Right, we never iterate over it, so instead
of moving the context to tls_device_down_list, we can remove it from
list, as long as we check to not remove it second time on destruction.

However, this way we don't gain anything, but lose a debugging
opportunity: for example, when list debugging is enabled, double
list_del will be detected.

So, it doesn't make sense to me to remove this list, but if you still
want to do it, Tariq has a patch for this.

> 
> We can delete it now if you don't have a preference, either way the fix
> is small.