linux-kernel - Re: [PATCH] net: sched: Fix an endian bug in tcf_proto

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Message-ID: <20231120100417.GM186930@vergenet.net>
Date:   Mon, 20 Nov 2023 10:04:17 +0000
From:   Simon Horman <horms@...nel.org>
To:     Pedro Tammela <pctammela@...atatu.com>
Cc:     Kunwu Chan <chentao@...inos.cn>, jhs@...atatu.com,
        xiyou.wangcong@...il.com, jiri@...nulli.us, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        kunwu.chan@...mail.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: sched: Fix an endian bug in tcf_proto_create

On Fri, Nov 17, 2023 at 09:06:45AM -0300, Pedro Tammela wrote:
> On 17/11/2023 06:31, Kunwu Chan wrote:
> > net/sched/cls_api.c:390:22: warning: incorrect type in assignment (different base types)
> > net/sched/cls_api.c:390:22:    expected restricted __be16 [usertype] protocol
> > net/sched/cls_api.c:390:22:    got unsigned int [usertype] protocol
> > 
> > Fixes: 33a48927c193 ("sched: push TC filter protocol creation into a separate function")
> > 
> > Signed-off-by: Kunwu Chan <chentao@...inos.cn>
> > ---
> >   net/sched/cls_api.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
> > index 1976bd163986..f73f39f61f66 100644
> > --- a/net/sched/cls_api.c
> > +++ b/net/sched/cls_api.c
> > @@ -387,7 +387,7 @@ static struct tcf_proto *tcf_proto_create(const char *kind, u32 protocol,
> >   		goto errout;
> >   	}
> >   	tp->classify = tp->ops->classify;
> > -	tp->protocol = protocol;
> > +	tp->protocol = cpu_to_be16(protocol);
> >   	tp->prio = prio;
> >   	tp->chain = chain;
> >   	spin_lock_init(&tp->lock);
> I don't believe there's something to fix here either

Hi Pedro and Kunwu,

I suspect that updating the byte order of protocol isn't correct
here - else I'd assume we would have seen a user-visible bug on
little-endian systems buy now.

But nonetheless I think there is a problem, which is that the appropriate
types aren't being used, which means the tooling isn't helping us wrt any
bugs that might subsequently be added or already lurking. So I think an
appropriate question is, what is the endien and width of protocol, and how
can we use an appropriate type throughout the call-path?