netdev - RE: [PATCH net-next] tls: Do not call sk_memcopy_from

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Date:   Fri, 21 Dec 2018 17:41:47 +0000
From:   Vakul Garg <vakul.garg@....com>
To:     David Miller <davem@...emloft.net>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "borisp@...lanox.com" <borisp@...lanox.com>,
        "aviadye@...lanox.com" <aviadye@...lanox.com>,
        "davejwatson@...com" <davejwatson@...com>,
        "doronrk@...com" <doronrk@...com>
Subject: RE: [PATCH net-next] tls: Do not call sk_memcopy_from_iter with zero
 length



> -----Original Message-----
> From: David Miller <davem@...emloft.net>
> Sent: Friday, December 21, 2018 10:39 PM
> To: Vakul Garg <vakul.garg@....com>
> Cc: netdev@...r.kernel.org; borisp@...lanox.com;
> aviadye@...lanox.com; davejwatson@...com; doronrk@...com
> Subject: Re: [PATCH net-next] tls: Do not call sk_memcopy_from_iter with
> zero length
> 
> From: Vakul Garg <vakul.garg@....com>
> Date: Fri, 21 Dec 2018 15:16:52 +0000
> 
> > @@ -943,10 +943,12 @@ int tls_sw_sendmsg(struct sock *sk, struct
> msghdr *msg, size_t size)
> >  				    tls_ctx->tx.overhead_size);
> >  		}
> >
> > -		ret = sk_msg_memcopy_from_iter(sk, &msg->msg_iter,
> msg_pl,
> > -					       try_to_copy);
> > -		if (ret < 0)
> > -			goto trim_sgl;
> > +		if (try_to_copy) {
> > +			ret = sk_msg_memcopy_from_iter(sk, &msg-
> >msg_iter,
> > +						       msg_pl, try_to_copy);
> > +			if (ret < 0)
> > +				goto trim_sgl;
> > +		}
> 
> This leaves 'ret' uninitialized, and the code below here uses it's value.

The variable 'ret' is already set to the return value of tls_clone_plaintext_msg().
In case try_to_copy != 0, the value of 'ret' is overwritten with return value of sk_msg_memcopy_from_iter().
In case try_to_copy == 0, the value of 'ret' remains same as the one set to  return value of tls_clone_plaintext_msg().
Subsequently, 'if (full_record || eor)' does not fufill, we continue and do not read 'ret'.
If 'if (full_record || eor)' evaluates true, value of ret is overwritten by return value of bpf_exec_tx_verdict().
So I do not find the problem.

Kindly advise if I am missing your point.