netdev - Re: [PATCH iproute2] iplink: work around rtattr length limits for IFLA_VFINFO

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Message-ID: <807bb557-6e0c-1567-026c-13becbaff9c2@gmail.com>
Date:   Sun, 17 Jan 2021 20:48:20 -0700
From:   David Ahern <dsahern@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>, Michal Kubecek <mkubecek@...e.cz>
Cc:     netdev@...r.kernel.org, Edwin Peer <edwin.peer@...adcom.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Andrew Gospodarek <andrew.gospodarek@...adcom.com>,
        Michael Chan <michael.chan@...adcom.com>
Subject: Re: [PATCH iproute2] iplink: work around rtattr length limits for
 IFLA_VFINFO_LIST

On 1/16/21 6:21 PM, Jakub Kicinski wrote:
> 
> I wonder. There is something inherently risky about making
> a precedent for user space depending on invalid kernel output.
> 
> _If_ we want to fix the kernel, IMO we should only fix the kernel.
> 

IMHO this is a kernel bug that should be fixed. An easy fix to check the
overflow in nla_nest_end and return an error. Sadly, nla_nest_end return
code is ignored and backporting any change to fix that will be
nightmare. A warning will identify places that need to be fixed.

We can at least catch and fix this overflow which is by far the primary
known victim of the rollover.