commit a4c1f3cc18df6fddd548f4df9f209695c4eb7263
Author: cinap_lenrek <cinap_lenrek@felloff.net>
Date:   Tue Nov 9 01:46:13 2021 +0000

    devtls: reject zero length records (thanks sigrid)
    
    zero length record causes ensure() todo nothing,
    while qgrab() assumes there is at least one buffer
    in the queue and would dereference the nil buffer.

diff --git a/sys/src/9/port/devtls.c b/sys/src/9/port/devtls.c
index 4b691c50e..e4974ec77 100644
--- a/sys/src/9/port/devtls.c
+++ b/sys/src/9/port/devtls.c
@@ -766,8 +766,8 @@ if(tr->debug)pprint("consumed %d header\n", RecHdrLen);
 	if(ver != tr->version && (tr->verset || ver < MinProtoVersion || ver > MaxProtoVersion))
 		rcvError(tr, EProtocolVersion, "devtls expected ver=%x%s, saw (len=%d) type=%x ver=%x '%.12s'",
 			tr->version, tr->verset?"/set":"", len, type, ver, (char*)header);
-	if(len > MaxCipherRecLen || len < 0)
-		rcvError(tr, ERecordOverflow, "record message too long %d", len);
+	if(len > MaxCipherRecLen || len <= 0)
+		rcvError(tr, ERecordOverflow, "bad record message length %d", len);
 	ensure(tr, &tr->unprocessed, len);
 	nconsumed = 0;
 	poperror();