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Message-ID: <20240717182733.GQ249423@kernel.org>
Date: Wed, 17 Jul 2024 19:27:33 +0100
From: Simon Horman <horms@...nel.org>
To: Guillaume Nault <gnault@...hat.com>
Cc: Stephen Hemminger <stephen@...workplumber.org>,
Maks Mishin <maks.mishinfz@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] f_flower: Remove always zero checks
On Wed, Jul 17, 2024 at 07:21:30PM +0200, Guillaume Nault wrote:
> On Wed, Jul 10, 2024 at 04:11:39PM -0700, Stephen Hemminger wrote:
> > On Sun, 7 Jul 2024 20:27:41 +0300
> > Maks Mishin <maks.mishinfz@...il.com> wrote:
> >
> > > Expression 'ttl & ~(255 >> 0)' is always zero, because right operand
> > > has 8 trailing zero bits, which is greater or equal than the size
> > > of the left operand == 8 bits.
> > >
> > > Found by RASU JSC.
> > >
> > > Signed-off-by: Maks Mishin <maks.mishinFZ@...il.com>
> > > ---
> > > tc/f_flower.c | 4 ++--
> > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/tc/f_flower.c b/tc/f_flower.c
> > > index 08c1001a..244f0f7e 100644
> > > --- a/tc/f_flower.c
> > > +++ b/tc/f_flower.c
> > > @@ -1523,7 +1523,7 @@ static int flower_parse_mpls_lse(int *argc_p, char ***argv_p,
> > >
> > > NEXT_ARG();
> > > ret = get_u8(&ttl, *argv, 10);
> > > - if (ret < 0 || ttl & ~(MPLS_LS_TTL_MASK >> MPLS_LS_TTL_SHIFT)) {
> > > + if (ret < 0) {
> > > fprintf(stderr, "Illegal \"ttl\"\n");
> > > return -1;
> > > }
> > > @@ -1936,7 +1936,7 @@ static int flower_parse_opt(const struct filter_util *qu, char *handle,
> > > }
> > > mpls_format_old = true;
> > > ret = get_u8(&ttl, *argv, 10);
> > > - if (ret < 0 || ttl & ~(MPLS_LS_TTL_MASK >> MPLS_LS_TTL_SHIFT)) {
> > > + if (ret < 0) {
> > > fprintf(stderr, "Illegal \"mpls_ttl\"\n");
> > > return -1;
> > > }
> >
> > That is correct mathematically, but perhaps the original author had different idea.
> > Could we have review from someone familiar with MPLS support please.
>
> The MPLS TTL field is an 8 bits value. Therefore any successful return
> of get_u8() should be valid and this test is indeed not needed.
>
> I guess the original intent was to keep consistency with how the other
> MPLS parameters are validated. But TTL is indeed a special case as it's
> the only parameter with a "common" length.
>
> Reviewed-by: Guillaume Nault <gnault@...hat.com>
Thanks Guillaume,
Yes, I agree that was very likely the intent.
Reviewed-by: Simon Horman <horms@...nel.org>
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