From 08ad57faa5802c8b902501cd52dfb33e991e849b Mon Sep 17 00:00:00 2001
From: alexandr nedvedicky - Sun Microsystems - Prague Czech Republic
 <alexandr.nedvedicky@oracle.com>
Date: Wed, 17 Apr 2019 09:44:24 +0200
Subject: [PATCH] fprintf(3) should not be used by signal handlers

On most OS platforms fprintf() et.al. are considered to be signal unsafe. I've
noticed the signal handlers in tcpdump call fprintf(). The patch below defers
call to fprintf() triggered by signal to pcap_loop callback.

Submitted to upstream:
https://github.com/the-tcpdump-group/tcpdump/issues/638

(fixes broken build on windows)

(s/ifdef/ifndef in my earlier change)
---
 tcpdump.c | 53 ++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 34 insertions(+), 19 deletions(-)

diff --git a/tcpdump.c b/tcpdump.c
index 52af74af5..062d6cbb5 100644
--- a/tcpdump.c
+++ b/tcpdump.c
@@ -217,8 +217,10 @@ static char *zflag = NULL;		/* compress each savefile using a specified command
 static int immediate_mode;
 #endif
 
-static int infodelay;
 static int infoprint;
+#ifndef _WIN32
+static int gotalarm;
+#endif /* _WIN32 */
 
 char *program_name;
 
@@ -2387,6 +2389,9 @@ DIAG_ON_CLANG(assign-enum)
 		 */
 		struct itimerval timer;
 		(void)setsignal(SIGALRM, verbose_stats_dump);
+		alarm(1);
+		/* signal alarm to get the first iteration ASAP */
+		gotalarm = 1;
 		timer.it_interval.tv_sec = 1;
 		timer.it_interval.tv_usec = 0;
 		timer.it_value.tv_sec = 1;
@@ -2738,8 +2743,6 @@ dump_packet_and_trunc(u_char *user, const struct pcap_pkthdr *h, const u_char *s
 
 	++packets_captured;
 
-	++infodelay;
-
 	dump_info = (struct dump_info *)user;
 
 	/*
@@ -2941,9 +2944,18 @@ dump_packet_and_trunc(u_char *user, const struct pcap_pkthdr *h, const u_char *s
 	if (dump_info->ndo != NULL)
 		pretty_print_packet(dump_info->ndo, h, sp, packets_captured);
 
-	--infodelay;
-	if (infoprint)
+	if (infoprint) {
 		info(0);
+		infoprint = 0;
+	}
+
+#ifndef _WIN32
+	if (gotalarm) {
+		fprintf(stderr, "Got %u\r", packets_captured);
+		gotalarm = 0;
+		alarm(1);
+	}
+#endif /* !_WIN32 */
 }
 
 static void
@@ -2953,8 +2965,6 @@ dump_packet(u_char *user, const struct pcap_pkthdr *h, const u_char *sp)
 
 	++packets_captured;
 
-	++infodelay;
-
 	dump_info = (struct dump_info *)user;
 
 	pcap_dump((u_char *)dump_info->pdd, h, sp);
@@ -2966,9 +2976,10 @@ dump_packet(u_char *user, const struct pcap_pkthdr *h, const u_char *sp)
 	if (dump_info->ndo != NULL)
 		pretty_print_packet(dump_info->ndo, h, sp, packets_captured);
 
-	--infodelay;
-	if (infoprint)
+	if (infoprint) {
 		info(0);
+		infoprint = 0;
+	}
 }
 
 static void
@@ -2976,23 +2987,27 @@ print_packet(u_char *user, const struct pcap_pkthdr *h, const u_char *sp)
 {
 	++packets_captured;
 
-	++infodelay;
-
 	pretty_print_packet((netdissect_options *)user, h, sp, packets_captured);
 
-	--infodelay;
-	if (infoprint)
+	if (infoprint) {
 		info(0);
+		infoprint = 0;
+	}
+
+#ifndef _WIN32
+	if (gotalarm) {
+		fprintf(stderr, "Got %u\r", packets_captured);
+		gotalarm = 0;
+		alarm(1);
+	}
+#endif /* !_WIN32 */
 }
 
 #ifdef SIGNAL_REQ_INFO
 static void
 requestinfo(int signo _U_)
 {
-	if (infodelay)
-		++infoprint;
-	else
-		info(0);
+	infoprint = 1;
 }
 #endif
 
@@ -3010,7 +3025,7 @@ print_packets_captured (void)
 {
 	static u_int prev_packets_captured, first = 1;
 
-	if (infodelay == 0 && (first || packets_captured != prev_packets_captured)) {
+	if (first || packets_captured != prev_packets_captured) {
 		fprintf(stderr, "Got %u\r", packets_captured);
 		first = 0;
 		prev_packets_captured = packets_captured;
@@ -3029,7 +3044,7 @@ static void CALLBACK verbose_stats_dump(PVOID param _U_,
 #else /* _WIN32 */
 static void verbose_stats_dump(int sig _U_)
 {
-	print_packets_captured();
+	gotalarm = 1;
 }
 #endif /* _WIN32 */