Re: [PATCH] net: sched: Fix an endian bug in tcf_proto_create

[Kunwu Chan]

Hi Simon,

Thanks for your reply.
For a lot of newcomers who aren't proficient in this part of the code, 
like me, it might be confusing what is the  correct endien and width of 
a protocol.

In response to your question, I wonder if it is necessary to implement a 
unified checking mechanism with a strict parameter validation for all 
invocation parameters?

For example, add an input parameter to the 'tcf_proto_create' to 
represent the endien and width of the protocol, and check the validity 
of the input parameter at the beginning of the function.

I don't have a good idea of how to make sure that the right type is used 
in the call path.
This is just my personal opinion, welcome to discuss.

On 2023/11/20 18:04, Simon Horman wrote:
> 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@xxxxxxxxxx>
> > > ---
> > >    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?