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Date:   Mon, 20 Nov 2023 10:04:17 +0000
From:   Simon Horman <horms@kernel.org>
To:     Pedro Tammela <pctammela@mojatatu.com>
Cc:     Kunwu Chan <chentao@kylinos.cn>, jhs@mojatatu.com,
        xiyou.wangcong@gmail.com, jiri@resnulli.us, davem@davemloft.net,
        edumazet@google.com, kuba@kernel.org, pabeni@redhat.com,
        kunwu.chan@hotmail.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] net: sched: Fix an endian bug in tcf_proto_create
Message-ID: <20231120100417.GM186930@vergenet.net>
References: <20231117093110.1842011-1-chentao@kylinos.cn>
 <16c758c6-479b-4c54-ad51-88c26a56b4c9@mojatatu.com>
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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@kylinos.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?