sctp: fix 'attempt to add with overflow' panic in dev profile (#393)

Author: cscorley

sctp/CHANGELOG.md

@@ -2,7 +2,8 @@
 
 ## Unreleased
 
-* Limit the bytes in the PendingQueue to avoid packets accumulating there uncontrollably [367](https://github.com/webrtc-rs/webrtc/pull/367).
+* Fix 'attempt to add with overflow' panic in dev profile [#393](https://github.com/webrtc-rs/webrtc/pull/393)
+* Limit the bytes in the PendingQueue to avoid packets accumulating there uncontrollably [#367](https://github.com/webrtc-rs/webrtc/pull/367).
 * Improve algorithm used to push to pending queue from O(n*log(n)) to O(log(n)) [#365](https://github.com/webrtc-rs/webrtc/pull/365).
 * Reuse as many allocations as possible when marshaling [#364](https://github.com/webrtc-rs/webrtc/pull/364).
 * The lock for the internal association was contended badly because marshaling was done while still in a critical section and also tokio was scheduling tasks badly [#363](https://github.com/webrtc-rs/webrtc/pull/363).

sctp/src/queue/reassembly_queue.rs

@@ -267,7 +267,8 @@ impl ReassemblyQueue {
                 return Err(Error::ErrTryAgain);
             }
             if cset.ssn == self.next_ssn {
-                self.next_ssn += 1;
+                // From RFC 4960 Sec 6.5:
+                self.next_ssn = self.next_ssn.wrapping_add(1);
             }
             self.ordered.remove(0)
         } else {
@@ -314,7 +315,7 @@ impl ReassemblyQueue {
 
         // Finally, forward next_ssn
         if sna16lte(self.next_ssn, last_ssn) {
-            self.next_ssn = last_ssn + 1;
+            self.next_ssn = last_ssn.wrapping_add(1);
         }
     }