diff mbox series

[ovs-dev,v3] dpif-netdev: Use unmasked key when adding datapath flows.

Message ID 166962558915.2312571.14121454926392179106.stgit@ebuild
State Accepted
Commit c82f496c3b69a036432af7c79adbc00545621ed1
Headers show
Series [ovs-dev,v3] dpif-netdev: Use unmasked key when adding datapath flows. | expand

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Commit Message

Eelco Chaudron Nov. 28, 2022, 8:53 a.m. UTC
The datapath supports installing wider flows, and OVS relies on
this behavior. For example if ipv4(src=1.1.1.1/192.0.0.0,
dst=1.1.1.2/192.0.0.0) exists, a wider flow (smaller mask) of
ipv4(src=192.1.1.1/128.0.0.0,dst=192.1.1.2/128.0.0.0) is allowed
to be added.

However, if we try to add a wildcard rule, the installation fails:

# ovs-appctl dpctl/add-flow system@myDP "in_port(1),eth_type(0x0800), \
  ipv4(src=1.1.1.1/192.0.0.0,dst=1.1.1.2/192.0.0.0,frag=no)" 2
# ovs-appctl dpctl/add-flow system@myDP "in_port(1),eth_type(0x0800), \
  ipv4(src=192.1.1.1/0.0.0.0,dst=49.1.1.2/0.0.0.0,frag=no)" 2
ovs-vswitchd: updating flow table (File exists)

The reason is that the key used to determine if the flow is already
present in the system uses the original key ANDed with the mask.
This results in the IP address not being part of the (miniflow) key,
i.e., being substituted with an all-zero value. When doing the actual
lookup, this results in the key wrongfully matching the first flow,
and therefore the flow does not get installed. The solution is to use
the unmasked key for the existence check, the same way this is handled
in the "slow" dpif_flow_put() case.

OVS relies on the fact that overlapping flows can exist if one is a
superset of the other. Note that this is only true when the same set
of actions is applied. This is due to how the revalidator process
works. During revalidation, OVS removes too generic flows from the
datapath to avoid incorrect matches but allows too narrow flows to
stay in the datapath to avoid the data plane disruption and also to
avoid constant flow deletions if the datapath ignores wildcards on
certain fields/bits.  See flow_wildcards_has_extra() check in the
revalidate_ukey__() function.

The problem here is that we have a too narrow flow installed, and now
OpenFlow rules got changed, so the actual flow should be more generic.
Revalidators will not remove the narrow flow, and we will eventually get
an upcall on the packet that doesn't match the narrow flow, but we will
not be able to install a more generic flow because after masking with
the new wider mask, the key matches on the narrow flow, so we get EEXIST.

Fixes: beb75a40fdc2 ("userspace: Switching of L3 packets in L2 pipeline")
Signed-off-by: Eelco Chaudron <echaudro@redhat.com>

---
v3:
  - Fixed comment text.
v2:
  - Updated commit message and added fixes tag.

 lib/dpif-netdev.c    |   33 +++++++++++++++++++++++++++++----
 tests/dpif-netdev.at |   14 ++++++++++++++
 2 files changed, 43 insertions(+), 4 deletions(-)

Comments

Ilya Maximets Dec. 20, 2022, 3:27 p.m. UTC | #1
On 11/28/22 09:53, Eelco Chaudron wrote:
> The datapath supports installing wider flows, and OVS relies on
> this behavior. For example if ipv4(src=1.1.1.1/192.0.0.0,
> dst=1.1.1.2/192.0.0.0) exists, a wider flow (smaller mask) of
> ipv4(src=192.1.1.1/128.0.0.0,dst=192.1.1.2/128.0.0.0) is allowed
> to be added.
> 
> However, if we try to add a wildcard rule, the installation fails:
> 
> # ovs-appctl dpctl/add-flow system@myDP "in_port(1),eth_type(0x0800), \
>   ipv4(src=1.1.1.1/192.0.0.0,dst=1.1.1.2/192.0.0.0,frag=no)" 2
> # ovs-appctl dpctl/add-flow system@myDP "in_port(1),eth_type(0x0800), \
>   ipv4(src=192.1.1.1/0.0.0.0,dst=49.1.1.2/0.0.0.0,frag=no)" 2
> ovs-vswitchd: updating flow table (File exists)
> 
> The reason is that the key used to determine if the flow is already
> present in the system uses the original key ANDed with the mask.
> This results in the IP address not being part of the (miniflow) key,
> i.e., being substituted with an all-zero value. When doing the actual
> lookup, this results in the key wrongfully matching the first flow,
> and therefore the flow does not get installed. The solution is to use
> the unmasked key for the existence check, the same way this is handled
> in the "slow" dpif_flow_put() case.
> 
> OVS relies on the fact that overlapping flows can exist if one is a
> superset of the other. Note that this is only true when the same set
> of actions is applied. This is due to how the revalidator process
> works. During revalidation, OVS removes too generic flows from the
> datapath to avoid incorrect matches but allows too narrow flows to
> stay in the datapath to avoid the data plane disruption and also to
> avoid constant flow deletions if the datapath ignores wildcards on
> certain fields/bits.  See flow_wildcards_has_extra() check in the
> revalidate_ukey__() function.
> 
> The problem here is that we have a too narrow flow installed, and now
> OpenFlow rules got changed, so the actual flow should be more generic.
> Revalidators will not remove the narrow flow, and we will eventually get
> an upcall on the packet that doesn't match the narrow flow, but we will
> not be able to install a more generic flow because after masking with
> the new wider mask, the key matches on the narrow flow, so we get EEXIST.
> 
> Fixes: beb75a40fdc2 ("userspace: Switching of L3 packets in L2 pipeline")
> Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
> 
> ---

Thanks!  Applied and backported down to 2.17.

Best regards, Ilya Maximets.
diff mbox series

Patch

diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index a45b46014..be2041ce2 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -3321,6 +3321,28 @@  netdev_flow_key_init_masked(struct netdev_flow_key *dst,
                             (dst_u64 - miniflow_get_values(&dst->mf)) * 8);
 }
 
+/* Initializes 'key' as a copy of 'flow'. */
+static inline void
+netdev_flow_key_init(struct netdev_flow_key *key,
+                     const struct flow *flow)
+{
+    uint64_t *dst = miniflow_values(&key->mf);
+    uint32_t hash = 0;
+    uint64_t value;
+
+    miniflow_map_init(&key->mf, flow);
+    miniflow_init(&key->mf, flow);
+
+    size_t n = dst - miniflow_get_values(&key->mf);
+
+    FLOW_FOR_EACH_IN_MAPS (value, flow, key->mf.map) {
+        hash = hash_add64(hash, value);
+    }
+
+    key->hash = hash_finish(hash, n * 8);
+    key->len = netdev_flow_key_size(n);
+}
+
 static inline void
 emc_change_entry(struct emc_entry *ce, struct dp_netdev_flow *flow,
                  const struct netdev_flow_key *key)
@@ -4195,7 +4217,7 @@  static int
 dpif_netdev_flow_put(struct dpif *dpif, const struct dpif_flow_put *put)
 {
     struct dp_netdev *dp = get_dp_netdev(dpif);
-    struct netdev_flow_key key, mask;
+    struct netdev_flow_key key;
     struct dp_netdev_pmd_thread *pmd;
     struct match match;
     ovs_u128 ufid;
@@ -4244,9 +4266,12 @@  dpif_netdev_flow_put(struct dpif *dpif, const struct dpif_flow_put *put)
 
     /* Must produce a netdev_flow_key for lookup.
      * Use the same method as employed to create the key when adding
-     * the flow to the dplcs to make sure they match. */
-    netdev_flow_mask_init(&mask, &match);
-    netdev_flow_key_init_masked(&key, &match.flow, &mask);
+     * the flow to the dplcs to make sure they match.
+     * We need to put in the unmasked key as flow_put_on_pmd() will first try
+     * to see if an entry exists doing a packet type lookup. As masked-out
+     * fields are interpreted as zeros, they could falsely match a wider IP
+     * address mask. Installation of the flow will use the match variable. */
+    netdev_flow_key_init(&key, &match.flow);
 
     if (put->pmd_id == PMD_ID_NULL) {
         if (cmap_count(&dp->poll_threads) == 0) {
diff --git a/tests/dpif-netdev.at b/tests/dpif-netdev.at
index 3179e1645..32054c52e 100644
--- a/tests/dpif-netdev.at
+++ b/tests/dpif-netdev.at
@@ -636,6 +636,20 @@  OVS_VSWITCHD_STOP(["/flow: in_port is not an exact match/d
 /failed to put/d"])
 AT_CLEANUP
 
+AT_SETUP([dpif-netdev - check dpctl/add-flow wider ip match])
+OVS_VSWITCHD_START(
+  [add-port br0 p1 \
+   -- set interface p1 type=dummy options:pstream=punix:$OVS_RUNDIR/p0.sock \
+   -- set bridge br0 datapath-type=dummy])
+
+AT_CHECK([ovs-appctl revalidator/pause])
+AT_CHECK([ovs-appctl dpctl/add-flow "in_port(1),eth_type(0x0800),ipv4(src=0.0.0.0/192.0.0.0,dst=0.0.0.0/192.0.0.0,frag=no)" "3"])
+AT_CHECK([ovs-appctl dpctl/add-flow "in_port(1),eth_type(0x0800),ipv4(src=192.1.1.1/0.0.0.0,dst=49.1.1.1/0.0.0.0,frag=no)" "3"])
+AT_CHECK([ovs-appctl revalidator/resume])
+
+OVS_VSWITCHD_STOP
+AT_CLEANUP
+
 # SEND_UDP_PKTS([p_name], [p_ofport])
 #
 # Sends 128 packets to port 'p_name' with different UDP destination ports.