iconvconfig: Fix behaviour with --prefix [BZ #28199]

The consolidation of configuration parsing broke behaviour with
--prefix, where the prefix bled into the modules cache.  Accept a
prefix which, when non-NULL, is prepended to the path when looking for
configuration files but only the original directory is added to the
modules cache.

This has no effect on the codegen of gconv_conf since it passes NULL.

Reported-by: Patrick McCarty <patrick.mccarty@intel.com>
Reported-by: Michael Hudson-Doyle <michael.hudson@canonical.com>
Reviewed-by: Andreas Schwab <schwab@linux-m68k.org>

iconv/gconv_conf.c

@@ -477,7 +477,7 @@ __gconv_read_conf (void)
   __gconv_get_path ();
 
   for (cnt = 0; __gconv_path_elem[cnt].name != NULL; ++cnt)
-    gconv_parseconfdir (__gconv_path_elem[cnt].name,
+    gconv_parseconfdir (NULL, __gconv_path_elem[cnt].name,
 			__gconv_path_elem[cnt].len);
 #endif
 

iconv/gconv_parseconfdir.h

@@ -39,7 +39,6 @@
 /* Name of the file containing the module information in the directories
    along the path.  */
 static const char gconv_conf_filename[] = "gconv-modules";
-static const char gconv_conf_dirname[] = "gconv-modules.d";
 
 static void add_alias (char *);
 static void add_module (char *, const char *, size_t, int);
@@ -110,19 +109,28 @@ read_conf_file (const char *filename, const char *directory, size_t dir_len)
   return true;
 }
 
+/* Prefix DIR (with length DIR_LEN) with PREFIX if the latter is non-NULL and
+   parse configuration in it.  */
+
 static __always_inline bool
-gconv_parseconfdir (const char *dir, size_t dir_len)
+gconv_parseconfdir (const char *prefix, const char *dir, size_t dir_len)
 {
-  /* No slash needs to be inserted between dir and gconv_conf_filename;
-     dir already ends in a slash.  */
-  char *buf = malloc (dir_len + sizeof (gconv_conf_dirname));
+  /* No slash needs to be inserted between dir and gconv_conf_filename; dir
+     already ends in a slash.  The additional 2 is to accommodate the ".d"
+     when looking for configuration files in gconv-modules.d.  */
+  size_t buflen = dir_len + sizeof (gconv_conf_filename) + 2;
+  char *buf = malloc (buflen + (prefix != NULL ? strlen (prefix) : 0));
+  char *cp = buf;
   bool found = false;
 
   if (buf == NULL)
     return false;
 
-  char *cp = mempcpy (mempcpy (buf, dir, dir_len), gconv_conf_filename,
-		      sizeof (gconv_conf_filename));
+  if (prefix != NULL)
+    cp = stpcpy (cp, prefix);
+
+  cp = mempcpy (mempcpy (cp, dir, dir_len), gconv_conf_filename,
+		sizeof (gconv_conf_filename));
 
   /* Read the gconv-modules configuration file first.  */
   found = read_conf_file (buf, dir, dir_len);

iconv/iconvconfig.c

@@ -652,13 +652,21 @@ add_module (char *rp, const char *directory,
 static int
 handle_dir (const char *dir)
 {
+  char *newp = NULL;
   size_t dirlen = strlen (dir);
   bool found = false;
 
-  char *fulldir = xasprintf ("%s%s%s", dir[0] == '/' ? prefix : "",
-			     dir, dir[dirlen - 1] != '/' ? "/" : "");
+  /* End directory path with a '/' if it doesn't already.  */
+  if (dir[dirlen - 1] != '/')
+    {
+      newp = xmalloc (dirlen + 2);
+      memcpy (newp, dir, dirlen);
+      newp[dirlen++] = '/';
+      newp[dirlen] = '\0';
+      dir = newp;
+    }
 
-  found = gconv_parseconfdir (fulldir, strlen (fulldir));
+  found = gconv_parseconfdir (dir[0] == '/' ? prefix : NULL, dir, dirlen);
 
   if (!found)
     {
@@ -670,7 +678,7 @@ handle_dir (const char *dir)
 	     "configuration files with names ending in .conf.");
     }
 
-  free (fulldir);
+  free (newp);
 
   return found ? 0 : 1;
 }