File tcpdump-CVE-2018-14879.patch of Package tcpdump.19046

From 9ba91381954ad325ea4fd26b9c65a8bd9a2a85b6 Mon Sep 17 00:00:00 2001
From: Denis Ovsienko <denis@ovsienko.info>
Date: Sun, 17 Jun 2018 22:15:19 +0100
Subject: [PATCH] (for 4.9.3) CVE-2018-14879/fix -V to fail invalid input
 safely

get_next_file() did not check the return value of strlen() and
underflowed an array index if the line read by fgets() from the file
started with \0. This caused an out-of-bounds read and could cause a
write. Add the missing check.

This vulnerability was discovered by Brian Carpenter & Geeknik Labs.
---
 tcpdump.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tcpdump.c b/tcpdump.c
index 128e41ed9..043bda1d7 100644
--- a/tcpdump.c
+++ b/tcpdump.c
@@ -699,13 +699,15 @@ static char *
 get_next_file(FILE *VFile, char *ptr)
 {
 	char *ret;
+	size_t len;
 
 	ret = fgets(ptr, PATH_MAX, VFile);
 	if (!ret)
 		return NULL;
 
-	if (ptr[strlen(ptr) - 1] == '\n')
-		ptr[strlen(ptr) - 1] = '\0';
+	len = strlen (ptr);
+	if (len > 0 && ptr[len - 1] == '\n')
+		ptr[len - 1] = '\0';
 
 	return ret;
 }