netdev - Re: [PATCH net-next,v2] net/tls: fix race condition causing kernel panic

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Message-ID: <20200525132534.1eeb2f55@kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net>
Date:   Mon, 25 May 2020 13:25:34 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vinay Kumar Yadav <vinay.yadav@...lsio.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, secdev@...lsio.com
Subject: Re: [PATCH net-next,v2] net/tls: fix race condition causing kernel
 panic

On Sat, 23 May 2020 01:40:31 +0530 Vinay Kumar Yadav wrote:
> tls_sw_recvmsg() and tls_decrypt_done() can be run concurrently.
> // tls_sw_recvmsg()
> 	if (atomic_read(&ctx->decrypt_pending))
> 		crypto_wait_req(-EINPROGRESS, &ctx->async_wait);
> 	else
> 		reinit_completion(&ctx->async_wait.completion);
> 
> //tls_decrypt_done()
>   	pending = atomic_dec_return(&ctx->decrypt_pending);
> 
>   	if (!pending && READ_ONCE(ctx->async_notify))
>   		complete(&ctx->async_wait.completion);
> 
> Consider the scenario tls_decrypt_done() is about to run complete()
> 
> 	if (!pending && READ_ONCE(ctx->async_notify))
> 
> and tls_sw_recvmsg() reads decrypt_pending == 0, does reinit_completion(),
> then tls_decrypt_done() runs complete(). This sequence of execution
> results in wrong completion. Consequently, for next decrypt request,
> it will not wait for completion, eventually on connection close, crypto
> resources freed, there is no way to handle pending decrypt response.
> 
> This race condition can be avoided by having atomic_read() mutually
> exclusive with atomic_dec_return(),complete().Intoduced spin lock to
> ensure the mutual exclution.
> 
> Addressed similar problem in tx direction.
> 
> v1->v2:
> - More readable commit message.
> - Corrected the lock to fix new race scenario.
> - Removed barrier which is not needed now.
> 
> Signed-off-by: Vinay Kumar Yadav <vinay.yadav@...lsio.com>

The tree should have been net, since this is a fix for:

Fixes: a42055e8d2c3 ("net/tls: Add support for async encryption of records for performance")

but admittedly it's not very urgent.

Reviewed-by: Jakub Kicinski <kuba@...nel.org>

We can try the trick with recording async_notify as a large bias 
on crypt_pending if the spin lock slows things down.