Hi Julian,
On Sun, Jun 12, 2016, at 02:09, Julian Anastasov wrote:
>
> Hello,
>
> On Sat, 11 Jun 2016, Hannes Frederic Sowa wrote:
>
> > Users of ToS rules could accidentally break ECN, this patch tries to
> > fix this in a way so we don't break shell scripts depending on the old
> > behavior while still being transparent to ECN. This quietly fixes ECN
> > behavior for old setups.
> >
> > For IPv6 we have no check if we check for ECN bits, in IPv4 we only
> > check for the last bit, which is specified to be '0' from pre-DSCP times
> > (because of implementation confusion).
> >
> > This patch changes fib rules in a way that matches only for ecn bits
> > will never match from now on (I consider them illegal), as we simply
> > ignore those rules (it was easier to explain in a pr_warn). Opinions?
>
> Well, may be the confusion comes from commit 89aef8921bfb
> ("ipv4: Delete routing cache.") where the 'tos &= IPTOS_RT_MASK;'
> line is lost from ip_route_input_common. I think, we should
> add it back, so that we can properly match input routes with rules
> that specify tos value. Old kernels didn't stored ECN bits in
> flowi4_tos in the input path, so we should do the same.
I would love to have done that but was fearing problems with user space
compatibility. Also IPTOS_RT_MASK is not enough for filtering, we need
to check for the whole INET_ECN_MASK.
>
> > Cc: Florian Westphal <f...@strlen.de>
> > Signed-off-by: Hannes Frederic Sowa <han...@stressinduktion.org>
> > ---
> > include/net/inet_ecn.h | 5 +++++
> > net/ipv4/fib_rules.c | 6 +++++-
> > net/ipv6/fib6_rules.c | 7 ++++++-
> > 3 files changed, 16 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/net/inet_ecn.h b/include/net/inet_ecn.h
> > index 0dc0a51da38faa..be65d94c05ee01 100644
> > --- a/include/net/inet_ecn.h
> > +++ b/include/net/inet_ecn.h
> > @@ -17,6 +17,11 @@ enum {
> >
> > extern int sysctl_tunnel_ecn_log;
> >
> > +static inline __u8 INET_ECN_ignore(__u8 dsfield)
> > +{
> > + return dsfield & ~INET_ECN_MASK;
> > +}
> > +
> > static inline int INET_ECN_is_ce(__u8 dsfield)
> > {
> > return (dsfield & INET_ECN_MASK) == INET_ECN_CE;
> > diff --git a/net/ipv4/fib_rules.c b/net/ipv4/fib_rules.c
> > index 6e9ea69e5f751b..87efbc38589c76 100644
> > --- a/net/ipv4/fib_rules.c
> > +++ b/net/ipv4/fib_rules.c
> > @@ -145,7 +145,8 @@ static int fib4_rule_match(struct fib_rule *rule,
> > struct flowi *fl, int flags)
> > ((daddr ^ r->dst) & r->dstmask))
> > return 0;
> >
> > - if (r->tos && (r->tos != fl4->flowi4_tos))
> > + if (!INET_ECN_ignore(r->tos) ||
>
> Above check will succeed for any rule that does not use
> tos (r->tos = 0). So, rules without tos will return 0 (no match).
Oh yes, certainly. I switched back and forth between different schemas.
This obviously doesn't work, thanks! I actually only tested the cases
with tos rules. :(
> > + INET_ECN_ignore(r->tos) != INET_ECN_ignore(fl4->flowi4_tos))
> > return 0;
>
> fib4_rule_configure already rejects ECN bits in r->tos,
> so no need to filter them again in fast path.
The problem is that IPTOS_TOS_MASK is just the masking of the 0x1 bit,
not both ECN bits. Thi stems from the pre-DSCP time where it was
forbidden to use bit 0x1 in TOS.
> > return 1;
> > @@ -215,6 +216,9 @@ static int fib4_rule_configure(struct fib_rule *rule,
> > struct sk_buff *skb,
> > rule4->dst_len = frh->dst_len;
> > rule4->dstmask = inet_make_mask(rule4->dst_len);
> > rule4->tos = frh->tos;
> > + if (!INET_ECN_ignore(rule4->tos))
> > + pr_warn("ipv4: never matching ipv4 rule with match for %x
> > added\n",
> > + rule4->tos);
>
> You should see this warning for non-tos rules...
I added the warnings after testing, sorry...
Bye,
Hannes
