From e3b4cb1b32c05ec668b16fe4e858e78b61fe5805 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Dag-Erling=20Sm=C3=B8rgrav?= <des@FreeBSD.org>
Date: Fri, 10 Mar 2023 13:24:36 +0000
Subject: [PATCH] tftpd: Use poll() instead of alarm() + setjmp().

While there, don't log an error when timing out waiting for a possible retransmit after a successful transfer.

Sponsored by:	Klara, Inc.
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D38966
---
 libexec/tftpd/tftp-io.c       | 38 +++++++++--------------------------
 libexec/tftpd/tftp-transfer.c |  2 +-
 2 files changed, 11 insertions(+), 29 deletions(-)

diff --git a/libexec/tftpd/tftp-io.c b/libexec/tftpd/tftp-io.c
index 4504946e910..a39b7cfe1fa 100644
--- a/libexec/tftpd/tftp-io.c
+++ b/libexec/tftpd/tftp-io.c
@@ -38,8 +38,7 @@ __FBSDID("$FreeBSD$");
 
 #include <assert.h>
 #include <errno.h>
-#include <setjmp.h>
-#include <signal.h>
+#include <poll.h>
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -377,27 +376,19 @@ send_data(int peer, uint16_t block, char *data, int size)
 
 /*
  * Receive a packet
+ *
+ * If timeout is negative, no error will be logged on timeout.
  */
-static jmp_buf timeoutbuf;
-
-static void
-timeout(int sig __unused)
-{
-
-	/* tftp_log(LOG_DEBUG, "Timeout\n");	Inside a signal handler... */
-	longjmp(timeoutbuf, 1);
-}
-
 int
 receive_packet(int peer, char *data, int size, struct sockaddr_storage *from,
-    int thistimeout)
+    int timeout)
 {
+	struct pollfd pfd;
 	struct tftphdr *pkt;
 	struct sockaddr_storage from_local;
 	struct sockaddr_storage *pfrom;
 	socklen_t fromlen;
 	int n;
-	static int timed_out;
 
 	if (debug & DEBUG_PACKETS)
 		tftp_log(LOG_DEBUG,
@@ -405,13 +396,11 @@ receive_packet(int peer, char *data, int size, struct sockaddr_storage *from,
 
 	pkt = (struct tftphdr *)data;
 
-	signal(SIGALRM, timeout);
-	timed_out = setjmp(timeoutbuf);
-	alarm(thistimeout);
-
-	if (timed_out != 0) {
-		tftp_log(LOG_ERR, "receive_packet: timeout");
-		alarm(0);
+	pfd.fd = peer;
+	pfd.events = POLLIN;
+	if (poll(&pfd, 1, 1000 * (timeout < 0 ? -timeout : timeout)) < 1) {
+		if (timeout > 0)
+			tftp_log(LOG_ERR, "receive_packet: timeout");
 		return (RP_TIMEOUT);
 	}
 
@@ -419,15 +408,8 @@ receive_packet(int peer, char *data, int size, struct sockaddr_storage *from,
 	fromlen = sizeof(*pfrom);
 	n = recvfrom(peer, data, size, 0, (struct sockaddr *)pfrom, &fromlen);
 
-	alarm(0);
-
 	DROPPACKETn("receive_packet", RP_TIMEOUT);
 
-	if (n < 0) {
-		tftp_log(LOG_ERR, "receive_packet: timeout");
-		return (RP_TIMEOUT);
-	}
-
 	if (n < 0) {
 		/* No idea what could have happened if it isn't a timeout */
 		tftp_log(LOG_ERR, "receive_packet: %s", strerror(errno));
diff --git a/libexec/tftpd/tftp-transfer.c b/libexec/tftpd/tftp-transfer.c
index 91f87a1159a..1949d00657b 100644
--- a/libexec/tftpd/tftp-transfer.c
+++ b/libexec/tftpd/tftp-transfer.c
@@ -436,7 +436,7 @@ tftp_receive(int peer, uint16_t *block, struct tftp_stats *ts,
 
 	for (i = 0; ; i++) {
 		n_data = receive_packet(peer, (char *)rp, pktsize,
-		    NULL, timeoutpacket);
+		    NULL, -timeoutpacket);
 		if (n_data <= 0)
 			break;
 		if (n_data > 0 &&
-- 
2.45.0