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List:       busybox
Subject:    [PATCH] nslookup: ensure unique transaction IDs for the DNS queries
From:       Uwe Kleine-König <uwe () kleine-koenig ! org>
Date:       2022-10-08 17:22:52
Message-ID: 20221008172252.3970941-1-uwe () kleine-koenig ! org
[Download RAW message or body]

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.
---
 networking/nslookup.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/networking/nslookup.c b/networking/nslookup.c
index 6da97baf4216..61e3eb6052ab 100644
--- a/networking/nslookup.c
+++ b/networking/nslookup.c
@@ -978,6 +978,10 @@ int nslookup_main(int argc UNUSED_PARAM, char **argv)
 		}
 	}
 
+	/* 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;
 
-- 
2.37.2

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