emacs/emacs-ctags-local-command-execute-vulnerability.patch

diff --git a/lib-src/etags.c b/lib-src/etags.c
index 588921bc70..a156444281 100644
--- a/lib-src/etags.c
+++ b/lib-src/etags.c
@@ -371,7 +371,7 @@ static void just_read_file (FILE *);

 static language *get_language_from_langname (const char *);
 static void readline (linebuffer *, FILE *);
-static long readline_internal (linebuffer *, FILE *, char const *);
+static long readline_internal (linebuffer *, FILE *, char const *, const bool);
 static bool nocase_tail (const char *);
 static void get_tag (char *, char **);
 static void get_lispy_tag (char *);
@@ -394,7 +394,9 @@ static void free_fdesc (fdesc *);
 static void pfnote (char *, bool, char *, int, int, long);
 static void invalidate_nodes (fdesc *, node **);
 static void put_entries (node *);
+static void clean_matched_file_tag (char const * const, char const * const);

+static void do_move_file (const char *, const char *);
 static char *concat (const char *, const char *, const char *);
 static char *skip_spaces (char *);
 static char *skip_non_spaces (char *);
@@ -1307,7 +1309,7 @@ main (int argc, char **argv)
 		  if (parsing_stdin)
 		    fatal ("cannot parse standard input "
 			   "AND read file names from it");
-		  while (readline_internal (&filename_lb, stdin, "-") > 0)
+		  while (readline_internal (&filename_lb, stdin, "-", false) > 0)
 		    process_file_name (filename_lb.buffer, lang);
 		}
 	      else
@@ -1355,9 +1357,6 @@ main (int argc, char **argv)
   /* From here on, we are in (CTAGS && !cxref_style) */
   if (update)
     {
-      char *cmd =
-	xmalloc (strlen (tagfile) + whatlen_max +
-		 sizeof "mv..OTAGS;grep -Fv '\t\t' OTAGS >;rm OTAGS");
       for (i = 0; i < current_arg; ++i)
 	{
 	  switch (argbuffer[i].arg_type)
@@ -1368,17 +1367,8 @@ main (int argc, char **argv)
 	    default:
 	      continue;		/* the for loop */
 	    }
-	  char *z = stpcpy (cmd, "mv ");
-	  z = stpcpy (z, tagfile);
-	  z = stpcpy (z, " OTAGS;grep -Fv '\t");
-	  z = stpcpy (z, argbuffer[i].what);
-	  z = stpcpy (z, "\t' OTAGS >");
-	  z = stpcpy (z, tagfile);
-	  strcpy (z, ";rm OTAGS");
-	  if (system (cmd) != EXIT_SUCCESS)
-	    fatal ("failed to execute shell command");
+	  clean_matched_file_tag (tagfile, argbuffer[i].what);
 	}
-      free (cmd);
       append_to_tagfile = true;
     }

@@ -1407,6 +1397,51 @@ main (int argc, char **argv)
   return EXIT_SUCCESS;
 }

+/*
+ * Equivalent to: mv tags OTAGS;grep -Fv ' filename ' OTAGS >tags;rm OTAGS
+ */
+static void
+clean_matched_file_tag (const char* tagfile, const char* match_file_name)
+{
+  FILE *otags_f = fopen ("OTAGS", "wb");
+  FILE *tag_f = fopen (tagfile, "rb");
+
+  if (otags_f == NULL)
+    pfatal ("OTAGS");
+
+  if (tag_f == NULL)
+    pfatal (tagfile);
+
+  int buf_len = strlen (match_file_name) + sizeof ("\t\t ") + 1;
+  char *buf = xmalloc (buf_len);
+  snprintf (buf, buf_len, "\t%s\t", match_file_name);
+
+  linebuffer line;
+  linebuffer_init (&line);
+  while (readline_internal (&line, tag_f, tagfile, true) > 0)
+    {
+      if (ferror (tag_f))
+        pfatal (tagfile);
+
+      if (strstr (line.buffer, buf) == NULL)
+        {
+          fprintf (otags_f, "%s\n", line.buffer);
+          if (ferror (tag_f))
+            pfatal (tagfile);
+        }
+    }
+  free (buf);
+  free (line.buffer);
+
+  if (fclose (otags_f) == EOF)
+    pfatal ("OTAGS");
+
+  if (fclose (tag_f) == EOF)
+    pfatal (tagfile);
+
+  do_move_file ("OTAGS", tagfile);
+  return;
+}

 /*
  * Return a compressor given the file name.  If EXTPTR is non-zero,
@@ -1794,7 +1829,7 @@ find_entries (FILE *inf)

   /* Else look for sharp-bang as the first two characters. */
   if (parser == NULL
-      && readline_internal (&lb, inf, infilename) > 0
+      && readline_internal (&lb, inf, infilename, false) > 0
       && lb.len >= 2
       && lb.buffer[0] == '#'
       && lb.buffer[1] == '!')
@@ -6293,7 +6328,7 @@ analyze_regex (char *regex_arg)
 	if (regexfp == NULL)
 	  pfatal (regexfile);
 	linebuffer_init (&regexbuf);
-	while (readline_internal (&regexbuf, regexfp, regexfile) > 0)
+	while (readline_internal (&regexbuf, regexfp, regexfile, false) > 0)
 	  analyze_regex (regexbuf.buffer);
 	free (regexbuf.buffer);
 	if (fclose (regexfp) != 0)
@@ -6648,11 +6683,13 @@ get_lispy_tag (register char *bp)

 /*
  * Read a line of text from `stream' into `lbp', excluding the
- * newline or CR-NL, if any.  Return the number of characters read from
- * `stream', which is the length of the line including the newline.
+ * newline or CR-NL (if `leave_cr` is false), if any.  Return the
+ * number of characters read from `stream', which is the length
+ * of the line including the newline.
  *
- * On DOS or Windows we do not count the CR character, if any before the
- * NL, in the returned length; this mirrors the behavior of Emacs on those
+ * On DOS or Windows, if `leave_cr` is false, we do not count the
+ * CR character, if any before the NL, in the returned length;
+ * this mirrors the behavior of Emacs on those
  * platforms (for text files, it translates CR-NL to NL as it reads in the
  * file).
  *
@@ -6660,7 +6697,7 @@ get_lispy_tag (register char *bp)
  * appended to `filebuf'.
  */
 static long
-readline_internal (linebuffer *lbp, FILE *stream, char const *filename)
+readline_internal (linebuffer *lbp, FILE *stream, char const *filename, const bool leave_cr)
 {
   char *buffer = lbp->buffer;
   char *p = lbp->buffer;
@@ -6691,7 +6728,7 @@ readline_internal (linebuffer *lbp, FILE *stream, char const *filename)
 	}
       if (c == '\n')
 	{
-	  if (p > buffer && p[-1] == '\r')
+	  if (!leave_cr && p > buffer && p[-1] == '\r')
 	    {
 	      p -= 1;
 	      chars_deleted = 2;
@@ -6736,7 +6773,7 @@ readline (linebuffer *lbp, FILE *stream)
   long result;

   linecharno = charno;		/* update global char number of line start */
-  result = readline_internal (lbp, stream, infilename); /* read line */
+  result = readline_internal (lbp, stream, infilename, false); /* read line */
   lineno += 1;			/* increment global line number */
   charno += result;		/* increment global char number */

@@ -7104,6 +7141,46 @@ etags_mktmp (void)
   return templt;
 }

+static void
+do_move_file(const char *src_file, const char *dst_file)
+{
+  if (rename (src_file, dst_file) == 0)
+    return;
+
+  FILE *src_f = fopen (src_file, "rb");
+  FILE *dst_f = fopen (dst_file, "wb");
+
+  if (src_f == NULL)
+    pfatal (src_file);
+
+  if (dst_f == NULL)
+    pfatal (dst_file);
+
+  int c;
+  while ((c = fgetc (src_f)) != EOF)
+    {
+      if (ferror (src_f))
+        pfatal (src_file);
+
+      if (ferror (dst_f))
+        pfatal (dst_file);
+
+      if (fputc (c, dst_f) == EOF)
+        pfatal ("cannot write");
+    }
+
+  if (fclose (src_f) == EOF)
+    pfatal (src_file);
+
+  if (fclose (dst_f) == EOF)
+    pfatal (dst_file);
+
+  if (unlink (src_file) == -1)
+    pfatal ("unlink error");
+
+  return;
+}
+
 /* Return a newly allocated string containing the file name of FILE
    relative to the absolute directory DIR (which should end with a slash). */
 static char *