From abecfdc298edfe2ef2c9d3d34742dcb80006a144 Mon Sep 17 00:00:00 2001
From: Artem Boldariev <artem@boldariev.com>
Date: Thu, 9 Sep 2021 16:52:55 +0300
Subject: [PATCH] DoT: do not attempt to call read callback if it is not
 avaialble

This commit fixes a crash in DoT code when it was attempting to call a
read callback on the later stages of the connection when it is not
available.

It also fixes [GL #2884] (back-trace provided in the bug report is
exactly the same as was seen when fixing this problem).
---
 lib/isc/netmgr/tlsdns.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lib/isc/netmgr/tlsdns.c b/lib/isc/netmgr/tlsdns.c
index 0d2828d4bf..72bb4ac4ba 100644
--- a/lib/isc/netmgr/tlsdns.c
+++ b/lib/isc/netmgr/tlsdns.c
@@ -940,6 +940,12 @@ isc__nm_tlsdns_processbuffer(isc_nmsocket_t *sock) {
 		return (ISC_R_NOMORE);
 	}
 
+	if (sock->recv_cb == NULL) {
+		/* recv_cb has been cleared - there is
+		 * nothing to do */
+		return (ISC_R_CANCELED);
+	}
+
 	req = isc__nm_get_read_req(sock, NULL);
 	REQUIRE(VALID_UVREQ(req));