[ovs-dev] [PATCH v5 ovn 4/4] ofctrl.c: Add a predictable resolution for conflicting flow actions.

Han Zhou hzhou at ovn.org
Tue Oct 13 07:23:51 UTC 2020


On Sun, Oct 11, 2020 at 5:06 AM Dumitru Ceara <dceara at redhat.com> wrote:
>
> Until now, in case the ACL configuration generates openflows that have
> the same match but different actions, ovn-controller was using the
> following approach:
> 1. If the flow being added contains conjunctive actions, merge its
>    actions with the already existing flow.
> 2. Otherwise, if the flow is being added incrementally
>    (update_installed_flows_by_track), don't install the new flow but
>    instead keep the old one.
> 3. Otherwise, (update_installed_flows_by_compare), don't install the
>    new flow but instead keep the old one.
>
> Even though one can argue that having an ACL with a match that includes
> the match of another ACL is a misconfiguration, it can happen that the
> users provision OVN like this.  Depending on the order of reading and
> installing the logical flows, the above operations can yield
> unpredictable results, e.g., allow specific traffic but then after
> ovn-controller is restarted (or a recompute happens) that specific
> traffic starts being dropped.
>
> A simple example of ACL configuration is:
> ovn-nbctl acl-add ls to-lport 3 '(ip4.src==10.0.0.1 ||
> ip4.src==10.0.0.2) && (ip4.dst == 10.0.0.3 || ip4.dst == 10.0.0.4)' allow
> ovn-nbctl acl-add ls to-lport 3 'ip4.src==10.0.0.1' allow
> ovn-nbctl acl-add ls to-lport 2 'arp' allow
> ovn-nbctl acl-add ls to-lport 1 'ip4' drop
>
> This is a pattern used by most CMSs:
> - define a default deny policy.
> - punch holes in the default deny policy based on user specific
>   configurations.
>
> Without this commit the behavior for traffic from 10.0.0.1 to 10.0.0.5
> is unpredictable.  Depending on the order of operations traffic might be
> dropped or allowed.
>
> It's also quite hard to force the CMS to ensure that such match overlaps
> never occur.
>
> To address this issue we now ensure that all desired flows refering the
same
> installed flow are partially sorted in the following way:
> - first all flows with action "allow".
> - then all flows with action "drop".
> - then a single flow with action "conjunction" (resulting from merging all
>   flows with the same match and action conjunction).
>
> This ensures that "allow" flows have precedence over "drop" flows which in
> turn have precedence over "conjunction" flows.  Essentially less
restrictive
> flows are always preferred over more restrictive flows whenever a match
> conflict happens.
>
> CC: Daniel Alvarez <dalvarez at redhat.com>
> Reported-at: https://bugzilla.redhat.com/1871931
> Signed-off-by: Dumitru Ceara <dceara at redhat.com>
> ---
>  controller/ofctrl.c |   95 +++++++++++++++++++---
>  tests/ovn.at        |  216
+++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 296 insertions(+), 15 deletions(-)
>
> diff --git a/controller/ofctrl.c b/controller/ofctrl.c
> index 74f98e3..30b5667 100644
> --- a/controller/ofctrl.c
> +++ b/controller/ofctrl.c
> @@ -172,6 +172,18 @@ struct sb_flow_ref {
>      struct uuid sb_uuid;
>  };
>
> +/* Desired flow reference type based on the action of the desired flow.
> + *
> + * This is used to maintain a partial ordering between multiple desired
> + * flows that are linked to the same installed flow.
> + */
> +enum desired_flow_ref_type {
> +    DFLOW_REF_ALLOW,
> +    DFLOW_REF_DROP,
> +    DFLOW_REF_CONJ,
> +    DFLOW_REF_MAX,
> +};
> +
>  /* A installed flow, in static variable installed_flows.
>   *
>   * Installed flows are updated in ofctrl_put for maintaining the flow
> @@ -188,6 +200,14 @@ struct sb_flow_ref {
>   * relationship is 1 to N. A link is added when a flow addition is
processed.
>   * A link is removed when a flow deletion is processed, the desired flow
>   * table is cleared, or the installed flow table is cleared.
> + *
> + * To ensure predictable behavior, the list of desired flows is
maintained
> + * partially sorted in the following way (from least restrictive to most
> + * restrictive wrt. match):
> + * - allow flows without action conjunction.
> + * - drop flows without action conjunction.
> + * - a single flow with action conjunction.
> + *
>   * The first desired_flow in the list is the active one, the one that is
>   * actually installed.
>   */
> @@ -195,12 +215,12 @@ struct installed_flow {
>      struct ovn_flow flow;
>      struct hmap_node match_hmap_node; /* For match based hashing. */
>
> -    /* A list of desired ovn_flow nodes (linked by
> +    /* Lists of desired ovn_flow nodes (linked by
>       * desired_flow.installed_ref_list_node), which reference this
installed
>       * flow.  (There are cases that multiple desired flows reference the
same
>       * installed flow, e.g. when there are conflict/duplicated ACLs that
>       * generates same match conditions). */
> -    struct ovs_list desired_refs;
> +    struct ovs_list desired_refs[DFLOW_REF_MAX];
>  };
>
>  typedef bool
> @@ -797,6 +817,12 @@ ofctrl_recv(const struct ofp_header *oh, enum
ofptype type)
>  }
>
>  static bool
> +flow_action_has_drop(const struct ovn_flow *f)
> +{
> +    return f->ofpacts_len == 0;
> +}
> +
> +static bool
>  flow_action_has_conj(const struct ovn_flow *f)
>  {
>      const struct ofpact *a = NULL;
> @@ -822,7 +848,18 @@ static bool
>  link_installed_to_desired(struct installed_flow *i, struct desired_flow
*d)
>  {
>      d->installed_flow = i;
> -    ovs_list_push_back(&i->desired_refs, &d->installed_ref_list_node);
> +
> +    if (flow_action_has_conj(&d->flow)) {
> +        ovs_assert(ovs_list_is_empty(&i->desired_refs[DFLOW_REF_CONJ]));
> +        ovs_list_push_back(&i->desired_refs[DFLOW_REF_CONJ],
> +                           &d->installed_ref_list_node);
> +    } else if (flow_action_has_drop(&d->flow)) {
> +        ovs_list_push_back(&i->desired_refs[DFLOW_REF_DROP],
> +                           &d->installed_ref_list_node);
> +    } else {
> +        ovs_list_push_back(&i->desired_refs[DFLOW_REF_ALLOW],
> +                           &d->installed_ref_list_node);
> +    }
>      return installed_flow_get_active(i) == d;
>  }
>
> @@ -854,15 +891,27 @@ unlink_installed_to_desired(struct installed_flow
*i, struct desired_flow *d)
>      ovs_assert(d && d->installed_flow == i);
>      ovs_list_remove(&d->installed_ref_list_node);
>      d->installed_flow = NULL;
> +
> +    /* If the flow we're removing was a conjunction flow, it should have
been
> +     * the only one referring this installed flow.
> +     */
> +    if (flow_action_has_conj(&d->flow)) {
> +        ovs_assert(ovs_list_is_empty(&i->desired_refs[DFLOW_REF_CONJ]));
> +    }
> +
>      return old_active == d;
>  }
>
>  static void
>  unlink_all_refs_for_installed_flow(struct installed_flow *i)
>  {
> -    struct desired_flow *d, *next;
> -    LIST_FOR_EACH_SAFE (d, next, installed_ref_list_node,
&i->desired_refs) {
> -        unlink_installed_to_desired(i, d);
> +    for (enum desired_flow_ref_type rt = 0; rt < DFLOW_REF_MAX; rt++) {
> +        struct desired_flow *d, *next;
> +
> +        LIST_FOR_EACH_SAFE (d, next, installed_ref_list_node,
> +                            &i->desired_refs[rt]) {
> +            unlink_installed_to_desired(i, d);
> +        }
>      }
>  }
>
> @@ -1253,7 +1302,10 @@ static struct installed_flow *
>  installed_flow_dup(struct desired_flow *src)
>  {
>      struct installed_flow *dst = xmalloc(sizeof *dst);
> -    ovs_list_init(&dst->desired_refs);
> +
> +    for (enum desired_flow_ref_type rt = 0; rt < DFLOW_REF_MAX; rt++) {
> +        ovs_list_init(&dst->desired_refs[rt]);
> +    }
>      dst->flow.table_id = src->flow.table_id;
>      dst->flow.priority = src->flow.priority;
>      minimatch_clone(&dst->flow.match, &src->flow.match);
> @@ -1267,10 +1319,12 @@ installed_flow_dup(struct desired_flow *src)
>  static struct desired_flow *
>  installed_flow_get_active(struct installed_flow *f)
>  {
> -    if (!ovs_list_is_empty(&f->desired_refs)) {
> -        return CONTAINER_OF(ovs_list_front(&f->desired_refs),
> -                            struct desired_flow,
> -                            installed_ref_list_node);
> +    for (enum desired_flow_ref_type rt = 0; rt < DFLOW_REF_MAX; rt++) {
> +        if (!ovs_list_is_empty(&f->desired_refs[rt])) {
> +            return CONTAINER_OF(ovs_list_front(&f->desired_refs[rt]),
> +                                struct desired_flow,
> +                                installed_ref_list_node);
> +        }
>      }
>      return NULL;
>  }
> @@ -1790,8 +1844,13 @@ update_installed_flows_by_compare(struct
ovn_desired_flow_table *flow_table,
>              link_installed_to_desired(i, d);
>          } else if (!d->installed_flow) {
>              /* This is a desired_flow that conflicts with one installed
> -             * previously but not linked yet. */
> -            link_installed_to_desired(i, d);
> +             * previously but not linked yet.  However, if this flow
becomes
> +             * active, e.g., it is less restrictive than the previous
active
> +             * flow then modify the installed flow.
> +             */
> +            if (link_installed_to_desired(i, d)) {
> +                installed_flow_mod(&i->flow, &d->flow, msgs);

Hi Dumitru, it seems ovn_flow_log() is missing here for the flow mod.

> +            }
>          }
>      }
>  }
> @@ -1920,8 +1979,14 @@ update_installed_flows_by_track(struct
ovn_desired_flow_table *flow_table,
>                  installed_flow_mod(&i->flow, &f->flow, msgs);
>              } else {
>                  /* Adding a new flow that conflicts with an existing
installed
> -                 * flow, so just add it to the link. */
> -                link_installed_to_desired(i, f);
> +                 * flow, so add it to the link.  If this flow becomes
active
> +                 * active, e.g., it is less restrictive than the previous
> +                 * active flow then modify the installed flow.
> +                 */
> +                if (link_installed_to_desired(i, f)) {
> +                    ovn_flow_log(&i->flow, "updating installed
(tracked)");
> +                    installed_flow_mod(&i->flow, &f->flow, msgs);
> +                }
>              }
>              /* The track_list_node emptyness is used to check if the
node is
>               * already added to track list, so initialize it again here.
*/
> diff --git a/tests/ovn.at b/tests/ovn.at
> index 6f1ab59..8202f38 100644
> --- a/tests/ovn.at
> +++ b/tests/ovn.at
> @@ -13727,6 +13727,222 @@ grep conjunction.*conjunction.*conjunction | wc
-l`])
>  OVN_CLEANUP([hv1])
>  AT_CLEANUP
>
> +AT_SETUP([ovn -- Superseeding ACLs with conjunction])
> +ovn_start
> +
> +ovn-nbctl ls-add ls1
> +
> +ovn-nbctl lsp-add ls1 ls1-lp1 \
> +-- lsp-set-addresses ls1-lp1 "f0:00:00:00:00:01"
> +
> +ovn-nbctl lsp-add ls1 ls1-lp2 \
> +-- lsp-set-addresses ls1-lp2 "f0:00:00:00:00:02"
> +
> +net_add n1
> +sim_add hv1
> +
> +as hv1
> +ovs-vsctl add-br br-phys
> +ovn_attach n1 br-phys 192.168.0.1
> +ovs-vsctl -- add-port br-int hv1-vif1 -- \
> +    set interface hv1-vif1 external-ids:iface-id=ls1-lp1 \
> +    options:tx_pcap=hv1/vif1-tx.pcap \
> +    options:rxq_pcap=hv1/vif1-rx.pcap \
> +    ofport-request=1
> +
> +ovs-vsctl -- add-port br-int hv1-vif2 -- \
> +    set interface hv1-vif2 external-ids:iface-id=ls1-lp2 \
> +    options:tx_pcap=hv1/vif2-tx.pcap \
> +    options:rxq_pcap=hv1/vif2-rx.pcap \
> +    ofport-request=2
> +
> +# test_ip INPORT SRC_MAC DST_MAC SRC_IP DST_IP OUTPORT...
> +#
> +# This shell function causes an ip packet to be received on INPORT.
> +# The packet's content has Ethernet destination DST and source SRC
> +# (each exactly 12 hex digits) and Ethernet type ETHTYPE (4 hex digits).
> +# The OUTPORTs (zero or more) list the VIFs on which the packet should
> +# be received.  INPORT and the OUTPORTs are specified as logical switch
> +# port numbers, e.g. 11 for vif11.
> +test_ip() {
> +    # This packet has bad checksums but logical L3 routing doesn't check.
> +    local inport=$1 src_mac=$2 dst_mac=$3 src_ip=$4 dst_ip=$5
> +    local
packet=${dst_mac}${src_mac}08004500001c0000000040110000${src_ip}\
> +${dst_ip}0035111100080000
> +    shift; shift; shift; shift; shift
> +    as hv1 ovs-appctl netdev-dummy/receive hv1-vif1 $packet
> +    for outport; do
> +        echo $packet >> $outport.expected
> +    done
> +}
> +
> +ip_to_hex() {
> +    printf "%02x%02x%02x%02x" "$@"
> +}
> +
> +reset_pcap_file() {
> +    local iface=$1
> +    local pcap_file=$2
> +    ovs-vsctl -- set Interface $iface options:tx_pcap=dummy-tx.pcap \
> +options:rxq_pcap=dummy-rx.pcap
> +    rm -f ${pcap_file}*.pcap
> +    ovs-vsctl -- set Interface $iface
options:tx_pcap=${pcap_file}-tx.pcap \
> +options:rxq_pcap=${pcap_file}-rx.pcap
> +}
> +
> +as hv1 ovn-appctl -t ovn-controller vlog/set ofctrl:dbg
> +
> +# Add a default deny ACL and an allow ACL for specific IP traffic.
> +ovn-nbctl acl-add ls1 to-lport 2 'arp' allow
> +ovn-nbctl acl-add ls1 to-lport 1 'ip4' drop
> +ovn-nbctl acl-add ls1 to-lport 3 '(ip4.src==10.0.0.1 ||
ip4.src==10.0.0.2) && (ip4.dst == 10.0.0.3 || ip4.dst == 10.0.0.4)' allow
> +ovn-nbctl acl-add ls1 to-lport 3 '(ip4.src==10.0.0.1 ||
ip4.src==10.0.0.42) && (ip4.dst == 10.0.0.3 || ip4.dst == 10.0.0.4)' allow
> +ovn-nbctl --wait=hv sync
> +
> +# Traffic 10.0.0.1, 10.0.0.2 -> 10.0.0.3, 10.0.0.4 should be allowed.
> +for src in `seq 1 2`; do
> +    for dst in `seq 3 4`; do
> +        sip=`ip_to_hex 10 0 0 $src`
> +        dip=`ip_to_hex 10 0 0 $dst`
> +
> +        test_ip 1 f00000000001 f00000000002 $sip $dip 2
> +    done
> +done
> +
> +# Traffic 10.0.0.1, 10.0.0.2 -> 10.0.0.5 should be dropped.
> +dip=`ip_to_hex 10 0 0 5`
> +for src in `seq 1 2`; do
> +    sip=`ip_to_hex 10 0 0 $src`
> +
> +    test_ip 1 f00000000001 f00000000002 $sip $dip
> +done
> +
> +cat 2.expected > expout
> +$PYTHON "$ovs_srcdir/utilities/ovs-pcap.in" hv1/vif2-tx.pcap > 2.packets
> +AT_CHECK([cat 2.packets], [0], [expout])
> +reset_pcap_file hv1-vif2 hv1/vif2
> +rm -f 2.packets
> +> 2.expected
> +
> +# Add two less restrictive allow ACLs for src IP 10.0.0.1.
> +ovn-nbctl acl-add ls1 to-lport 3 'ip4.src==10.0.0.1 ||
ip4.src==10.0.0.1' allow
> +ovn-nbctl acl-add ls1 to-lport 3 'ip4.src==10.0.0.1' allow
> +ovn-nbctl --wait=hv sync
> +
> +# Check OVS flows, the less restrictive flows should have been installed.
> +AT_CHECK([as hv1 ovs-ofctl dump-flows br-int table=45 | \
> +    grep "priority=1003" | awk '{print $7 " " $8}' | sort], [0], [dnl
> +priority=1003,conj_id=2,ip,metadata=0x1 actions=resubmit(,46)
> +priority=1003,conj_id=3,ip,metadata=0x1 actions=resubmit(,46)
> +priority=1003,ip,metadata=0x1,nw_dst=10.0.0.3
actions=conjunction(2,1/2),conjunction(3,1/2)
> +priority=1003,ip,metadata=0x1,nw_dst=10.0.0.4
actions=conjunction(2,1/2),conjunction(3,1/2)
> +priority=1003,ip,metadata=0x1,nw_src=10.0.0.1 actions=resubmit(,46)
> +priority=1003,ip,metadata=0x1,nw_src=10.0.0.2 actions=conjunction(2,2/2)
> +priority=1003,ip,metadata=0x1,nw_src=10.0.0.42 actions=conjunction(3,2/2)
> +])
> +
> +# Traffic 10.0.0.1, 10.0.0.2 -> 10.0.0.3, 10.0.0.4 should be allowed.
> +for src in `seq 1 2`; do
> +    for dst in `seq 3 4`; do
> +        sip=`ip_to_hex 10 0 0 $src`
> +        dip=`ip_to_hex 10 0 0 $dst`
> +
> +        test_ip 1 f00000000001 f00000000002 $sip $dip 2
> +    done
> +done
> +
> +# Traffic 10.0.0.2 -> 10.0.0.5 should be dropped.
> +sip=`ip_to_hex 10 0 0 2`
> +dip=`ip_to_hex 10 0 0 5`
> +test_ip 1 f00000000001 f00000000002 $sip $dip
> +
> +# Traffic 10.0.0.1 -> 10.0.0.5 should be allowed.
> +sip=`ip_to_hex 10 0 0 1`
> +dip=`ip_to_hex 10 0 0 5`
> +test_ip 1 f00000000001 f00000000002 $sip $dip 2
> +
> +cat 2.expected > expout
> +$PYTHON "$ovs_srcdir/utilities/ovs-pcap.in" hv1/vif2-tx.pcap > 2.packets
> +AT_CHECK([cat 2.packets], [0], [expout])
> +reset_pcap_file hv1-vif2 hv1/vif2
> +rm -f 2.packets
> +> 2.expected
> +
> +#sleep infinity
> +
> +# Remove the first less restrictive allow ACL.
> +ovn-nbctl acl-del ls1 to-lport 3 'ip4.src==10.0.0.1 || ip4.src==10.0.0.1'
> +ovn-nbctl --wait=hv sync
> +
> +# Check OVS flows, the second less restrictive allow ACL should have
been installed.
> +AT_CHECK([as hv1 ovs-ofctl dump-flows br-int table=45 | \
> +    grep "priority=1003" | awk '{print $7 " " $8}' | sort], [0], [dnl
> +priority=1003,conj_id=2,ip,metadata=0x1 actions=resubmit(,46)
> +priority=1003,conj_id=3,ip,metadata=0x1 actions=resubmit(,46)
> +priority=1003,ip,metadata=0x1,nw_dst=10.0.0.3
actions=conjunction(2,1/2),conjunction(3,1/2)
> +priority=1003,ip,metadata=0x1,nw_dst=10.0.0.4
actions=conjunction(2,1/2),conjunction(3,1/2)
> +priority=1003,ip,metadata=0x1,nw_src=10.0.0.1 actions=resubmit(,46)
> +priority=1003,ip,metadata=0x1,nw_src=10.0.0.2 actions=conjunction(2,2/2)
> +priority=1003,ip,metadata=0x1,nw_src=10.0.0.42 actions=conjunction(3,2/2)
> +])
> +
> +# Remove the less restrictive allow ACL.
> +ovn-nbctl acl-del ls1 to-lport 3 'ip4.src==10.0.0.1'
> +ovn-nbctl --wait=hv sync
> +
> +# Check OVS flows, the 10.0.0.1 conjunction should have been reinstalled.
> +AT_CHECK([as hv1 ovs-ofctl dump-flows br-int table=45 | \
> +    grep "priority=1003" | awk '{print $7 " " $8}' | sort], [0], [dnl
> +priority=1003,conj_id=2,ip,metadata=0x1 actions=resubmit(,46)
> +priority=1003,conj_id=3,ip,metadata=0x1 actions=resubmit(,46)
> +priority=1003,ip,metadata=0x1,nw_dst=10.0.0.3
actions=conjunction(2,1/2),conjunction(3,1/2)
> +priority=1003,ip,metadata=0x1,nw_dst=10.0.0.4
actions=conjunction(2,1/2),conjunction(3,1/2)
> +priority=1003,ip,metadata=0x1,nw_src=10.0.0.1
actions=conjunction(2,2/2),conjunction(3,2/2)
> +priority=1003,ip,metadata=0x1,nw_src=10.0.0.2 actions=conjunction(2,2/2)
> +priority=1003,ip,metadata=0x1,nw_src=10.0.0.42 actions=conjunction(3,2/2)
> +])
> +
> +# Traffic 10.0.0.1, 10.0.0.2 -> 10.0.0.3, 10.0.0.4 should be allowed.
> +for src in `seq 1 2`; do
> +    for dst in `seq 3 4`; do
> +        sip=`ip_to_hex 10 0 0 $src`
> +        dip=`ip_to_hex 10 0 0 $dst`
> +
> +        test_ip 1 f00000000001 f00000000002 $sip $dip 2
> +    done
> +done
> +
> +# Traffic 10.0.0.1, 10.0.0.2 -> 10.0.0.5 should be dropped.
> +dip=`ip_to_hex 10 0 0 5`
> +for src in `seq 1 2`; do
> +    sip=`ip_to_hex 10 0 0 $src`
> +
> +    test_ip 1 f00000000001 f00000000002 $sip $dip
> +done
> +
> +cat 2.expected > expout
> +$PYTHON "$ovs_srcdir/utilities/ovs-pcap.in" hv1/vif2-tx.pcap > 2.packets
> +AT_CHECK([cat 2.packets], [0], [expout])
> +
> +# Re-add the less restrictive allow ACL for src IP 10.0.0.1
> +ovn-nbctl acl-add ls1 to-lport 3 'ip4.src==10.0.0.1' allow
> +ovn-nbctl --wait=hv sync
> +
> +# Check OVS flows, the less restrictive flows should have been installed.
> +AT_CHECK([as hv1 ovs-ofctl dump-flows br-int table=45 | \
> +   grep "priority=1003" | awk '{print $7 " " $8}' | sort], [0], [dnl
> +priority=1003,conj_id=2,ip,metadata=0x1 actions=resubmit(,46)
> +priority=1003,conj_id=3,ip,metadata=0x1 actions=resubmit(,46)
> +priority=1003,ip,metadata=0x1,nw_dst=10.0.0.3
actions=conjunction(2,1/2),conjunction(3,1/2)
> +priority=1003,ip,metadata=0x1,nw_dst=10.0.0.4
actions=conjunction(2,1/2),conjunction(3,1/2)
> +priority=1003,ip,metadata=0x1,nw_src=10.0.0.1 actions=resubmit(,46)
> +priority=1003,ip,metadata=0x1,nw_src=10.0.0.2 actions=conjunction(2,2/2)
> +priority=1003,ip,metadata=0x1,nw_src=10.0.0.42 actions=conjunction(3,2/2)
> +])
> +
> +OVN_CLEANUP([hv1])
> +AT_CLEANUP
> +
>  # 3 hypervisors, one logical switch, 3 logical ports per hypervisor
>  AT_SETUP([ovn -- L2 Drop and Allow ACL w/ Stateful ACL])
>  ovn_start
>


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