busybox: nslookup: ensure unique transaction IDs for the DNS queries

On machines with a coarse monotonic clock (here: TP-Link RE200 powered
by a MediaTek MT7620A) it can happen that the two DNS requests (for A
and AAAA) share the same transaction ID. If this happens the second
reply is wrongly dropped and nslookup reports "No answer".

Fix this by ensuring that the transaction IDs are unique.

Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>

diff --git a/package/utils/busybox/patches/530-nslookup-ensure-unique-transaction-IDs-for-the-DNS-queries.patch b/package/utils/busybox/patches/530-nslookup-ensure-unique-transaction-IDs-for-the-DNS-queries.patch
new file mode 100644 (file)
index 0000000..caa5ee7
--- /dev/null
+++ b/package/utils/busybox/patches/530-nslookup-ensure-unique-transaction-IDs-for-the-DNS-queries.patch
@@ -0,0 +1,42 @@
+From: Uwe Kleine-König <uwe@kleine-koenig.org>
+Date: Sat, 8 Oct 2022 19:22:52 +0200
+Subject: [PATCH] nslookup: ensure unique transaction IDs for the DNS queries
+
+The transaction IDs generated by res_mkquery() for both glibc and musl only
+depends on the state of the monotonic clock.
+For some machines (here: a TP-Link RE200 powered by a MediaTek MT7620A)
+the monotonic clock has a coarse resolution (here: 20 µs) and it can happen
+that the requests for A and AAAA share the same transaction ID.
+
+In that case the mapping from received responses to the sent queries
+doesn't work and name resolution fails as follows:
+
+        # /bin/busybox nslookup heise.de
+        Server:         127.0.0.1
+        Address:        127.0.0.1:53
+
+        Non-authoritative answer:
+        Name:   heise.de
+        Address: 193.99.144.80
+
+        *** Can't find heise.de: No answer
+
+because the AAAA reply is dropped as a duplicate reply to the A query.
+
+To prevent this make sure the transaction IDs are unique.
+
+Forwarded: http://lists.busybox.net/pipermail/busybox/2022-October/089911.html
+---
+--- a/networking/nslookup.c
++++ b/networking/nslookup.c
+@@ -978,6 +978,10 @@ int nslookup_main(int argc UNUSED_PARAM,
+               }
+       }
+ 
++      /* Ensure the Transaction IDs are unique */
++      for (rc = 1; rc < G.query_count; rc++)
++              G.query[rc].query[1] = G.query[rc - 1].query[1] + 1;
++
+       for (rc = 0; rc < G.serv_count;) {
+               int c;
+