netdev - Re: [net] net/tls: fix corrupted data in recvmsg

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Message-ID: <20201114195437.4d0493b2@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Sat, 14 Nov 2020 19:54:37 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vadim Fedorenko <vfedorenko@...ek.ru>
Cc:     Boris Pismenny <borisp@...dia.com>,
        Aviad Yehezkel <aviadye@...dia.com>, netdev@...r.kernel.org
Subject: Re: [net] net/tls: fix corrupted data in recvmsg

Please don't top post.

On Sun, 15 Nov 2020 02:26:30 +0000 Vadim Fedorenko wrote:
> No, I don't have any BPFs in test.
> If we have Application Data in TCP queue then tls_sw_advance_skb
> will change ctx->control from 0x16 to 0x17 (TLS_RECORD_TYPE_DATA)
> and the loop will continue.

Ah! Missed that, unpausing the parser will make it serve us another
message and overwrite ctx.

> The patched if will make zc = true and
> data will be decrypted into msg->msg_iter.
> After that the loop will break on:
>                  if (!control)
>                          control = tlm->control;
>                  else if (control != tlm->control)
>                          goto recv_end;
>
> and the data will be lost.
> Next call to recvmsg will find ctx->decrypted set to true and will
> copy the unencrypted data from skb assuming that it has been decrypted
> already.
> 
> The patch that I put into Fixes: changed the check you mentioned to
> ctx->control, but originally it was checking the value of control that
> was stored before calling to tls_sw_advance_skb.

Is there a reason why we wouldn't just go back to checking the stored
control? Or better - put your condition there (control != ctx->control)?
Decrypting the next record seems unnecessary given we can't return it.