ofctrl: Do not try to program long flows

If the flow size is bigger than UINT16_MAX it doesn't
fit into openflow message. Programming of such flow will
fail which results in disconnect of ofctrl. After reconnect
we program everything from scratch, in case the long flow still
remains the cycle continues. This causes the node to be almost
unusable as there will be massive traffic disruptions.

To prevent that check if the flow is within the allowed size.
If not log the flow that would trigger this problem and do not program
it. This isn't a self-healing process, but the chance of this happening
are very slim. Also, any flow that is bigger than allowed size is OVN
bug, and it should be fixed.

Reported-at: https://bugzilla.redhat.com/1955167
Signed-off-by: Ales Musil <amusil@redhat.com>
Signed-off-by: Mark Michelson <mmichels@redhat.com>

controller/ofctrl.c

@@ -16,6 +16,7 @@
 #include <config.h>
 #include "bitmap.h"
 #include "byte-order.h"
+#include "coverage.h"
 #include "dirs.h"
 #include "dp-packet.h"
 #include "flow.h"
@@ -55,6 +56,8 @@
 
 VLOG_DEFINE_THIS_MODULE(ofctrl);
 
+COVERAGE_DEFINE(ofctrl_msg_too_long);
+
 /* An OpenFlow flow. */
 struct ovn_flow {
     /* Key. */
@@ -1769,6 +1772,18 @@ ovn_flow_log(const struct ovn_flow *f, const char *action)
     }
 }
 
+static void
+ovn_flow_log_size_err(const struct ovn_flow *f)
+{
+    COVERAGE_INC(ofctrl_msg_too_long);
+
+    static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(5, 1);
+
+    char *s = ovn_flow_to_string(f);
+    VLOG_ERR_RL(&rl, "The FLOW_MOD message is too big: %s", s);
+    free(s);
+}
+
 static void
 ovn_flow_uninit(struct ovn_flow *f)
 {
@@ -1888,15 +1903,27 @@ encode_bundle_add(struct ofpbuf *msg, struct ofputil_bundle_ctrl_msg *bc)
     return ofputil_encode_bundle_add(OFP15_VERSION, &bam);
 }
 
-static void
+static bool
 add_flow_mod(struct ofputil_flow_mod *fm,
              struct ofputil_bundle_ctrl_msg *bc,
              struct ovs_list *msgs)
 {
     struct ofpbuf *msg = encode_flow_mod(fm);
     struct ofpbuf *bundle_msg = encode_bundle_add(msg, bc);
+
+    uint32_t flow_mod_len = msg->size;
+    uint32_t bundle_len = bundle_msg->size;
+
     ofpbuf_delete(msg);
+
+    if (flow_mod_len > UINT16_MAX || bundle_len > UINT16_MAX) {
+        ofpbuf_delete(bundle_msg);
+
+        return false;
+    }
+
     ovs_list_push_back(msgs, &bundle_msg->list_node);
+    return true;
 }
 
 /* group_table. */
@@ -2235,7 +2262,10 @@ installed_flow_add(struct ovn_flow *d,
         .new_cookie = htonll(d->cookie),
         .command = OFPFC_ADD,
     };
-    add_flow_mod(&fm, bc, msgs);
+
+    if (!add_flow_mod(&fm, bc, msgs)) {
+        ovn_flow_log_size_err(d);
+    }
 }
 
 static void
@@ -2259,14 +2289,18 @@ installed_flow_mod(struct ovn_flow *i, struct ovn_flow *d,
         /* Use OFPFC_ADD so that cookie can be updated. */
         fm.command = OFPFC_ADD;
     }
-    add_flow_mod(&fm, bc, msgs);
+    bool result = add_flow_mod(&fm, bc, msgs);
 
     /* Replace 'i''s actions and cookie by 'd''s. */
     mem_stats.installed_flow_usage -= i->ofpacts_len - d->ofpacts_len;
     free(i->ofpacts);
     i->ofpacts = xmemdup(d->ofpacts, d->ofpacts_len);
     i->ofpacts_len = d->ofpacts_len;
     i->cookie = d->cookie;
+
+    if (!result) {
+        ovn_flow_log_size_err(i);
+    }
 }
 
 static void
@@ -2280,7 +2314,10 @@ installed_flow_del(struct ovn_flow *i,
         .table_id = i->table_id,
         .command = OFPFC_DELETE_STRICT,
     };
-    add_flow_mod(&fm, bc, msgs);
+
+    if (!add_flow_mod(&fm, bc, msgs)) {
+        ovn_flow_log_size_err(i);
+    }
 }
 
 static void