From 130775cd16d74401a2206218e2dc0f32d1c59898 Mon Sep 17 00:00:00 2001
From: michael <info@komika.org>
Date: Tue, 1 Feb 2022 14:41:20 +0000
Subject: [PATCH] net: improve error handling in dnsclient_unix.go

In the file net/dnsclient_unix.go in the function newRequest
error handling is missing after calling b.Finish(). If
the implementation of dnsmessage.Builder.Finish changes
it is theoretically possible that the missing error handling
introduces a nil pointer exception.

Fixes #50946

Change-Id: I3f0785f71def6649d6089d0af71c9e50f5ccb259
GitHub-Last-Rev: 2a2197f7e6d18d5477967b299ed734a7b224536d
GitHub-Pull-Request: golang/go#50948
Reviewed-on: https://go-review.googlesource.com/c/go/+/381966
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
---
 src/net/dnsclient_unix.go | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/net/dnsclient_unix.go b/src/net/dnsclient_unix.go
index 15dbc258302..17435365907 100644
--- a/src/net/dnsclient_unix.go
+++ b/src/net/dnsclient_unix.go
@@ -74,11 +74,14 @@ func newRequest(q dnsmessage.Question) (id uint16, udpReq, tcpReq []byte, err er
 	}
 
 	tcpReq, err = b.Finish()
+	if err != nil {
+		return 0, nil, nil, err
+	}
 	udpReq = tcpReq[2:]
 	l := len(tcpReq) - 2
 	tcpReq[0] = byte(l >> 8)
 	tcpReq[1] = byte(l)
-	return id, udpReq, tcpReq, err
+	return id, udpReq, tcpReq, nil
 }
 
 func checkResponse(reqID uint16, reqQues dnsmessage.Question, respHdr dnsmessage.Header, respQues dnsmessage.Question) bool {