From b4736c90adb84032aaf1e3bcb8988916a82ed5de Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dag-Erling=20Sm=C3=B8rgrav?= <des@FreeBSD.org>
Date: Fri, 10 Mar 2023 13:24:44 +0000
Subject: [PATCH] tftpd: Don't consume arbitrary requests when failing to fork.

We've already consumed one request, which is sufficient to prevent inetd from endlessly restarting us in this particular and extremely unlikely case.

Sponsored by:	Klara, Inc.
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D38967
---
 libexec/tftpd/tftpd.c | 52 ++++++++++---------------------------------
 1 file changed, 12 insertions(+), 40 deletions(-)

diff --git a/libexec/tftpd/tftpd.c b/libexec/tftpd/tftpd.c
index 4b8a3024fe5a..8e3d2e13f320 100644
--- a/libexec/tftpd/tftpd.c
+++ b/libexec/tftpd/tftpd.c
@@ -134,7 +134,8 @@ main(int argc, char *argv[])
 	struct passwd	*nobody;
 	const char	*chuser = "nobody";
 	char		recvbuffer[MAXPKTSIZE];
-	int		allow_ro = 1, allow_wo = 1;
+	int		allow_ro = 1, allow_wo = 1, on = 1;
+	pid_t		pid;
 
 	tzset();			/* syslog in localtime */
 	acting_as_client = 0;
@@ -222,12 +223,9 @@ main(int argc, char *argv[])
 
 	umask(mask);
 
-	{
-		int on = 1;
-		if (ioctl(0, FIONBIO, &on) < 0) {
-			tftp_log(LOG_ERR, "ioctl(FIONBIO): %s", strerror(errno));
-			exit(1);
-		}
+	if (ioctl(0, FIONBIO, &on) < 0) {
+		tftp_log(LOG_ERR, "ioctl(FIONBIO): %s", strerror(errno));
+		exit(1);
 	}
 
 	/* Find out who we are talking to and what we are going to do */
@@ -255,40 +253,14 @@ main(int argc, char *argv[])
 	 * break before doing the above "recvfrom", inetd would
 	 * spawn endless instances, clogging the system.
 	 */
-	{
-		int i, pid;
-
-		for (i = 1; i < 20; i++) {
-		    pid = fork();
-		    if (pid < 0) {
-				sleep(i);
-				/*
-				 * flush out to most recently sent request.
-				 *
-				 * This may drop some request, but those
-				 * will be resent by the clients when
-				 * they timeout.  The positive effect of
-				 * this flush is to (try to) prevent more
-				 * than one tftpd being started up to service
-				 * a single request from a single client.
-				 */
-				peerlen = sizeof peer_sock;
-				i = recvfrom(0, recvbuffer, MAXPKTSIZE, 0,
-				    (struct sockaddr *)&peer_sock, &peerlen);
-				if (i > 0) {
-					n = i;
-				}
-		    } else {
-				break;
-		    }
-		}
-		if (pid < 0) {
-			tftp_log(LOG_ERR, "fork: %s", strerror(errno));
-			exit(1);
-		} else if (pid != 0) {
-			exit(0);
-		}
+	pid = fork();
+	if (pid < 0) {
+		tftp_log(LOG_ERR, "fork: %s", strerror(errno));
+		exit(1);
+	} else if (pid != 0) {
+		exit(0);
 	}
+	/* child */
 
 #ifdef	LIBWRAP
 	/*