[ovs-dev] [PATCH] netdev-linux: Be more careful about integer overflow in policing.

Ben Pfaff blp at nicira.com
Fri Mar 13 18:31:10 UTC 2015


On Tue, Mar 10, 2015 at 09:28:22PM -0700, Ansis Atteka wrote:
> On Tue, Mar 10, 2015 at 1:37 PM, Ben Pfaff <blp at nicira.com> wrote:
> > Otherwise the policing limits could make no sense if large rates were
> > specified.
> >
> > Reported-by: Zhangguanghui <zhang.guanghui at h3c.com>
> > Signed-off-by: Ben Pfaff <blp at nicira.com>
> > ---
> >  AUTHORS            |    1 +
> >  lib/netdev-linux.c |   13 +++++++------
> >  vswitchd/bridge.c  |    4 ++--
> >  3 files changed, 10 insertions(+), 8 deletions(-)
> >
> > diff --git a/AUTHORS b/AUTHORS
> > index 6e8b4da..00627ef 100644
> > --- a/AUTHORS
> > +++ b/AUTHORS
> > @@ -344,6 +344,7 @@ Voravit T.              voravit at kth.se
> >  Yeming Zhao             zhaoyeming at gmail.com
> >  Ying Chen               yingchen at vmware.com
> >  Yongqiang Liu           liuyq7809 at gmail.com
> > +Zhangguanghui           zhang.guanghui at h3c.com
> >  Ziyou Wang              ziyouw at vmware.com
> >  Zolt??n Balogh           zoltan.balogh at ericsson.com
> >  ankur dwivedi           ankurengg2003 at gmail.com
> > diff --git a/lib/netdev-linux.c b/lib/netdev-linux.c
> > index 920c884..199e6ac 100644
> > --- a/lib/netdev-linux.c
> > +++ b/lib/netdev-linux.c
> > @@ -1,5 +1,5 @@
> >  /*
> > - * Copyright (c) 2009, 2010, 2011, 2012, 2013, 2014 Nicira, Inc.
> > + * Copyright (c) 2009, 2010, 2011, 2012, 2013, 2014, 2015 Nicira, Inc.
> >   *
> >   * Licensed under the Apache License, Version 2.0 (the "License");
> >   * you may not use this file except in compliance with the License.
> > @@ -405,8 +405,8 @@ static struct tcmsg *tc_make_request(const struct netdev *, int type,
> >                                       unsigned int flags, struct ofpbuf *);
> >  static int tc_transact(struct ofpbuf *request, struct ofpbuf **replyp);
> >  static int tc_add_del_ingress_qdisc(struct netdev *netdev, bool add);
> > -static int tc_add_policer(struct netdev *netdev, int kbits_rate,
> > -                          int kbits_burst);
> > +static int tc_add_policer(struct netdev *,
> > +                          uint32_t kbits_rate, uint32_t kbits_burst);
> >
> >  static int tc_parse_qdisc(const struct ofpbuf *, const char **kind,
> >                            struct nlattr **options);
> > @@ -4525,7 +4525,8 @@ tc_add_del_ingress_qdisc(struct netdev *netdev, bool add)
> >   * Returns 0 if successful, otherwise a positive errno value.
> >   */
> >  static int
> > -tc_add_policer(struct netdev *netdev, int kbits_rate, int kbits_burst)
> > +tc_add_policer(struct netdev *netdev,
> > +               uint32_t kbits_rate, uint32_t kbits_burst)
> >  {
> >      struct tc_police tc_police;
> >      struct ofpbuf request;
> > @@ -4539,8 +4540,8 @@ tc_add_policer(struct netdev *netdev, int kbits_rate, int kbits_burst)
> >      tc_police.action = TC_POLICE_SHOT;
> >      tc_police.mtu = mtu;
> >      tc_fill_rate(&tc_police.rate, ((uint64_t) kbits_rate * 1000)/8, mtu);
> > -    tc_police.burst = tc_bytes_to_ticks(tc_police.rate.rate,
> > -                                        kbits_burst * 1024);
> > +    tc_police.burst = tc_bytes_to_ticks(
> > +        tc_police.rate.rate, MIN(UINT32_MAX / 1024, kbits_burst) * 1024);
> 
> Maybe silly questions, since I actually did not try out the code, but
> 1. is it correct that above kbits_burst is multiplied with 1024, but
> in tc_fill_rate()  kbits_rate is multiplied with 1000?
> 2. also, tc_fill_rate() above seems to init tc_police.rate in bytes
> not bits, but tc_bytes_to_ticks() expects both arguments to be in same
> units to cancel out?

It's definitely weird, but testing shows that it does the right thing
at least from "tc filter show"'s point of view.  How about if I add
this comment?

    /* The following appears wrong in two ways:
     *
     * - tc_bytes_to_ticks() should take "bytes" as quantity for both of its
     *   arguments (or at least consistently "bytes" as both or "bits" as
     *   both), but this supplies bytes for the first argument and bits for the
     *   second.
     *
     * - In networking a kilobit is usually 1000 bits but this uses 1024 bits.
     *
     * However if you "fix" those problems then "tc filter show ..." shows
     * "125000b", meaning 125,000 bits, when OVS configures it for 1000 kbit ==
     * 1,000,000 bits, so while this actually ends up doing the right thing
     * from tc's point of view.  Whatever. */



More information about the dev mailing list