netdev - RE: [PATCH v2 net-next 1/2] net: dsa: lan9303: Add port_fast_age and port_fdb

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6DD009D4AB@AcuExch.aculab.com>
Date:   Fri, 20 Oct 2017 08:59:52 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Egil Hjelmeland' <privat@...l-hjelmeland.no>,
        'Andrew Lunn' <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...oirfairelinux.com>
CC:     "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 net-next 1/2] net: dsa: lan9303: Add port_fast_age
 and port_fdb_dump methods

From: Egil Hjelmeland
> Sent: 19 October 2017 17:53
...
> >> IMHO it is best to define a struct for the 'ctx and then do:
> >>     ..., void *v_ctx)
> >> {
> >>     foo_ctx *ctx = v_ctx;
> >>     int port = ctx->port;
> >>
> >> That stops anyone having to double-check that the *(int *)
> >> is operating on a pointer to an integer of the correct size.
> >>
> >
> > Does casting to a struct pointer require less manual double-check than
> > to a int-pointer? In neither cases the compiler can protect us, IFAIK.
> > But on the other hand, a the text "foo_ctx" can searched in the editor.
> > So in that respect it can somewhat aid to the double-checking.
> >
> > So I can do that.
> >
> >
> 
> I understand now that the caller side (lan9303_port_fast_age) is
> vulnerable. Say somebody has the idea to change the "port" param
> of .port_fast_age from int to u8, then my code is a trap.

Worse, change it to a long and it will work on everything except
64bit big-endian systems.

	David