From a6dfd2015c202f3424eb58846d8575a877728881 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dag-Erling=20Sm=C3=B8rgrav?= <des@FreeBSD.org>
Date: Fri, 10 Mar 2023 13:24:15 +0000
Subject: [PATCH] tftpd: Fix max block size calculation.

Sponsored by:	Klara, Inc.
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D38953
---
 libexec/tftpd/tftp-options.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/libexec/tftpd/tftp-options.c b/libexec/tftpd/tftp-options.c
index 01876b4750f..037517f9cd7 100644
--- a/libexec/tftpd/tftp-options.c
+++ b/libexec/tftpd/tftp-options.c
@@ -230,6 +230,7 @@ option_blksize(int peer)
 		tftp_log(LOG_ERR, "sysctl: net.inet.udp.maxdgram");
 		return (acting_as_client ? 1 : 0);
 	}
+	maxdgram -= 4; /* leave room for header */
 
 	int size = atoi(options[OPT_BLKSIZE].o_request);
 	if (size < BLKSIZE_MIN || size > BLKSIZE_MAX) {