netdev - Re: [PATCH net 5/5] tls: don't decrypt the next record if it's of a different type

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Date: Tue, 12 Sep 2023 12:38:35 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Sabrina Dubroca <sd@...asysnail.net>
Cc: Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
	Dave Watson <davejwatson@...com>, Vakul Garg <vakul.garg@....com>,
	Boris Pismenny <borisp@...dia.com>,
	John Fastabend <john.fastabend@...il.com>
Subject: Re: [PATCH net 5/5] tls: don't decrypt the next record if it's of a
 different type

On Fri, Sep 08, 2023 at 05:38:49PM +0200, Sabrina Dubroca wrote:
>
> tls_decrypt_done only runs the completion when decrypt_pending drops
> to 0, so this should be covered.

That doesn't look very safe.  What if the first decrypt completes
before the second decrypt even starts? Wouldn't that cause two
complete calls on ctx->async_wait?

> I wonder if this situation could happen:
> 
> tls_sw_recvmsg
>   process first record
>     decrypt_pending = 1
>                                   CB runs
>                                   decrypt_pending = 0
>                                   complete(&ctx->async_wait.completion);
> 
>   process second record
>     decrypt_pending = 1
>   tls_sw_recvmsg reaches "recv_end"
>     decrypt_pending != 0
>     crypto_wait_req sees the first completion of ctx->async_wait and proceeds
> 
>                                   CB runs
>                                   decrypt_pending = 0
>                                   complete(&ctx->async_wait.completion);

Yes that's exactly what I was thinking of.

I think this whole thing needs some rethinking and rewriting.

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt