rx: Introduce ack_is_valid

[openafs.git] / src / rx / rx.c

diff --git a/src/rx/rx.c b/src/rx/rx.c
index 73fb9c8..76d7d69 100644 (file)
--- a/src/rx/rx.c
+++ b/src/rx/rx.c
@@ -4249,6 +4249,41 @@ rx_ack_reason(int reason)
 }
 #endif
 
+static_inline int
+ack_is_valid(struct rx_call *call, afs_uint32 first, afs_uint32 prev)
+{
+    if (first < call->tfirst) {
+       /*
+        * The peer indicated that the window went backwards. That's not
+        * allowed; the window can only move forwards.
+        */
+       return 0;
+    }
+
+    if (first == call->tfirst && prev < call->tprev) {
+       /*
+        * The peer said the last DATA packet it received was seq X, but it
+        * already told us before that it had received data after X. This is
+        * probably just an out-of-order ACK, and so we can ignore it.
+        */
+       if (prev >= call->tfirst + call->twind) {
+           /*
+            * Some peers (OpenAFS libafs before 1.6.23) mistakenly set the
+            * previousPacket field to a serial number, not a sequence number.
+            * The sequence number the peer told us about is further than our
+            * transmit window, so it cannot possibly be correct; it's probably
+            * actually a serial number. Don't ignore packets based on this;
+            * the previousPacket information is not accurate.
+            */
+           return 1;
+       }
+
+       return 0;
+    }
+
+    /* Otherwise, the ack looks valid. */
+    return 1;
+}
 
 /* The real smarts of the whole thing.  */
 static struct rx_packet *
@@ -4287,14 +4322,7 @@ rxi_ReceiveAckPacket(struct rx_call *call, struct rx_packet *np,
     prev = ntohl(ap->previousPacket);
     serial = ntohl(ap->serial);
 
-    /*
-     * Ignore ack packets received out of order while protecting
-     * against peers that set the previousPacket field to a packet
-     * serial number instead of a sequence number.
-     */
-    if (first < call->tfirst ||
-        (first == call->tfirst && prev < call->tprev && prev < call->tfirst
-        + call->twind)) {
+    if (!ack_is_valid(call, first, prev)) {
        return np;
     }