[groff] 02/13: [xtotroff]: Avoid overrunning buffer write.

[G. Branden Robinson]

gbranden pushed a commit to branch master
in repository groff.

commit 29385650a04a339dbb49b684eb7b2d40ed5b6beb
Author: G. Branden Robinson <g.branden.robinson@gmail.com>
AuthorDate: Tue Dec 1 16:37:16 2020 +1100

    [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=].
---
 ChangeLog                     | 9 +++++++++
 src/utils/xtotroff/xtotroff.c | 7 +++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 0b63af5..0e03a30 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,14 @@
 2020-12-01  G. Branden Robinson <g.branden.robinson@gmail.com>
 
+       * 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().
+
+2020-12-01  G. Branden Robinson <g.branden.robinson@gmail.com>
+
        * src/utils/xtotroff/xtotroff.c (CanonicalizeFontName,
        FontNamesAmbiguous, MapFont, main): Format diagnostic messages
        more consistently with GNU Coding Standards.  Prefix with name
diff --git a/src/utils/xtotroff/xtotroff.c b/src/utils/xtotroff/xtotroff.c
index f6d316d..cf7c41b 100644
--- a/src/utils/xtotroff/xtotroff.c
+++ b/src/utils/xtotroff/xtotroff.c
@@ -130,7 +130,9 @@ 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];
@@ -161,7 +163,8 @@ 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))