Re: [PATCH net-next v2 1/1] taprio: Add boundary check for sched-entry values

[Vladimir Oltean]

On Thu, Oct 19, 2023 at 12:35:30PM +0200, Paolo Abeni wrote:
> On Wed, 2023-10-18 at 19:56 +0200, Gerhard Engleder wrote:
> > On 18.10.23 05:28, Lai Peter Jun Ann wrote:
> > > Adds boundary checks for the gatemask provided against the number of
> > > traffic class defined for each sched-entry.
> > > 
> > > Without this check, the user would not know that the gatemask provided is
> > > invalid and the driver has already truncated the gatemask provided to
> > > match the number of traffic class defined.
> > > 
> > > Signed-off-by: Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@xxxxxxxxx>
> > > Signed-off-by: Michael Sit Wei Hong <michael.wei.hong.sit@xxxxxxxxx>
> > > Signed-off-by: Lai Peter Jun Ann <jun.ann.lai@xxxxxxxxx>
> > > ---
> > >   net/sched/sch_taprio.c | 8 ++++++++
> > >   1 file changed, 8 insertions(+)
> > > 
> > > diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
> > > index 1cb5e41..44b9e21 100644
> > > --- a/net/sched/sch_taprio.c
> > > +++ b/net/sched/sch_taprio.c
> > > @@ -102,6 +102,7 @@ struct taprio_sched {
> > >   	u32 max_sdu[TC_MAX_QUEUE]; /* save info from the user */
> > >   	u32 fp[TC_QOPT_MAX_QUEUE]; /* only for dump and offloading */
> > >   	u32 txtime_delay;
> > > +	u8 num_tc;

To the patch: I would oppose introducing an "u8 num_tc" to struct
taprio_sched for one purpose only. It is a duplication of
netdev->num_tc, the only problem is that it hasn't yet been set, which
can be solved with a bit of code reorganization.

> > >   };
> > >   
> > >   struct __tc_taprio_qopt_offload {
> > > @@ -1063,6 +1064,11 @@ static int fill_sched_entry(struct taprio_sched *q, struct nlattr **tb,
> > >   		return -EINVAL;
> > >   	}
> > >   
> > > +	if (entry->gate_mask >= q->num_tc) {
> > 
> > As far as I know within gate_mask every bit represents a traffic class.
> > So for 3 traffic classes at gate_mask of 0x7 is valid but this check
> > fails with 0x7 >= 3.
> 
> Additionally whatever check we put in place previously just ignored by
> the existing code, could break the existing user-space: we can't accept
> such change. 

I agree, and I would oppose erroring out.

I used to have this patch which simply masks off the excess bits,
calling netdev_warn() - which can be transformed into a warning netlink
extack - instead.
https://patchwork.kernel.org/project/netdevbpf/patch/20230130173145.475943-15-vladimir.oltean@xxxxxxx/

I didn't have a strong motivation for the patch, and I dropped it.
If Lai Peter Jun Ann can come with the motivation, we can go with that
approach.