From: Maria Matejka <mq@ucw.cz>
Date: Fri, 14 Nov 2025 19:11:59 +0000 (+0100)
Subject: Channel: Fix race condition of a new feed with an update in the table
X-Git-Tag: v3.2.0~16
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e6c699d29dd7d82f887cf38f59c36ee268e6293b;p=thirdparty%2Fbird.git

Channel: Fix race condition of a new feed with an update in the table

In case an update arrived while another thread feeding anew, there was
a race condition causing the old route to be counted against the export limit
despite never reached.

In long run, this caused limit counter underflow and a hard assertion failure.
---

diff --git a/nest/rt-table.c b/nest/rt-table.c
index 8cb052bf5..9141ddc6c 100644
--- a/nest/rt-table.c
+++ b/nest/rt-table.c
@@ -1463,6 +1463,9 @@ channel_notify_any(void *_channel)
 
 	      if (old)
 	      {
+		/* There are more old routes but these we should have
+		 * never seen these newer old routes because we haven't
+		 * seen the appropriate journal items */
 		EXPORT_FLAG_EXPECT(c, oo, accepted, 0);
 		EXPORT_FLAG_EXPECT(c, oo, rejected, 0);
 		oo->src = NULL;
@@ -1471,6 +1474,15 @@ channel_notify_any(void *_channel)
 		old = oo;
 	    }
 
+	    /* Check whether the old route was actually seen because this may
+	     * an initial feed. */
+	    bool oacc = old && bmap_test(&c->export_accepted_map, old->id);
+	    bool orej = old && bmap_test(&c->export_rejected_map, old->id);
+
+	    /* Not seen */
+	    if (!oacc && !orej)
+	      old = NULL;
+
 	    /* Invalid routes become withdraws */
 	    if (!rte_is_valid(new))
 	      new = NULL;