From 1fce38a3b2dc10c5bdd2c9f97c08c66dce7f0a95 Mon Sep 17 00:00:00 2001
From: "G. Branden Robinson" <g.branden.robinson@gmail.com>
Date: Tue, 1 Dec 2020 16:37:16 +1100
Subject: [PATCH 6/7] [xtotroff]: Avoid overrunning buffer write.

* src/utils/xtotroff/xtotroff.c (MapFont): Avoid writing past
  the end of a static buffer.  Problem found and patch supplied by
  Bjarni Ingi Gislason.  I tweaked it to comment it differently (in case
  the buffer ever needs to grow, but the prospects of future X11
  server-side font rendering development seem dim) and use snprintf()
  instead of retaining the existing sprintf().

  Quiets warning: '%s' directive writing up to 255 bytes into a region
  of size between 0 and 255 [-Wformat-overflow=].
---
 src/utils/xtotroff/xtotroff.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/utils/xtotroff/xtotroff.c b/src/utils/xtotroff/xtotroff.c
index 8545a5e..aee2a1a 100644
--- a/src/utils/xtotroff/xtotroff.c
+++ b/src/utils/xtotroff/xtotroff.c
@@ -127,7 +127,9 @@ static int MapFont(char *font_name, const char *troff_name)
   XFontName parsed;
   int j, k;
   DviCharNameMap *char_map;
-  char encoding[256];
+  /* 'encoding' needs to hold a CharSetRegistry (256), a CharSetEncoding
+     (256) [both from XFontName.h], a dash, and a null terminator. */
+  char encoding[256 * 2 + 1 + 1];
   char *s;
   int wid;
   char name_string[2048];
@@ -156,7 +158,8 @@ static int MapFont(char *font_name, const char *troff_name)
     return 0;
 
   XParseFontName(names[0], &parsed, &attributes);
-  sprintf(encoding, "%s-%s", parsed.CharSetRegistry,
+  size_t sz = sizeof encoding;
+  snprintf(encoding, sz, "%s-%s", parsed.CharSetRegistry,
 	  parsed.CharSetEncoding);
   for (s = encoding; *s; s++)
     if (isupper(*s))
-- 
2.32.0