netdev - RE: [net-next 1/1] tipc: enforce valid ratio between skb truesize and contents

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Date:   Tue, 21 Nov 2017 12:17:20 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jon Maloy' <jon.maloy@...csson.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "mohan.krishna.ghanta.krishnamurthy@...csson.com" 
        <mohan.krishna.ghanta.krishnamurthy@...csson.com>,
        "tung.q.nguyen@...tech.com.au" <tung.q.nguyen@...tech.com.au>,
        "hoang.h.le@...tech.com.au" <hoang.h.le@...tech.com.au>,
        "canh.d.luu@...tech.com.au" <canh.d.luu@...tech.com.au>,
        "ying.xue@...driver.com" <ying.xue@...driver.com>,
        "tipc-discussion@...ts.sourceforge.net" 
        <tipc-discussion@...ts.sourceforge.net>
Subject: RE: [net-next  1/1] tipc: enforce valid ratio between skb truesize
 and contents

From: Jon Maloy
> Sent: 15 November 2017 20:24
> The socket level flow control is based on the assumption that incoming
> buffers meet the condition (skb->truesize / roundup(skb->len) <= 4),
> where the latter value is rounded off upwards to the nearest 1k number.
> This does empirically hold true for the device drivers we know, but we
> cannot trust that it will always be so, e.g., in a system with jumbo
> frames and very small packets.

I'd be more worried about drivers that set skb->truesize to the amount
of data in the skb rather than the memory used by the skb.

Last I looked some of the usbnet drivers lied badly.

	David