Fix bug 64823: ZTS GD fails to to find system TrueType font

First, the `$fontfile` parameter actually supports a semicolon
delimited list of fonts (as documented[1]); thus passing the full
string to `VCWD_REALPATH()` or `php_check_open_basedir()` makes no
sense; we could pass the individual parts, but …

Second, libgd uses an elaborate font detection.  There is a hard-
coded `DEFAULT_PATH` which can be overridden by the environment
variable `GDFONTPATH`.  Semantics are like the `PATH` environment
variable.  If `DEFAULT_PATH` was still exposed (it is no longer as of
libgd 2.1.0[2]), we could take that into account, but …

External libgd can be configured with font-config support, so font
aliases and even lookup patterns are supported.  There is no way to
cater to that upfront.

Thus, we no longer interfere with libgd's font lookup.  Checking the
realpath was already doubtful (we didn't even use the resolved path).
Lifting the open_basedir restriction is a bit more delicate, but the
manual still states that open_basedir would not apply, and more
relevant, not much harm can be done, because libgd only passes the
found font to `FT_New_Face()` which likely fails for any non font files
without any error which could reveal sensitive information.  And the
font file is never written.

It should be noted that this solves lookup of system fonts, does not
change the behavior for absolute font paths, but still does not resolve
issues with relative paths to font files in ZTS environments using
external libgd (our bundled libgd has a workaround for that).  This
particular issue cannot be solved, so users of ZTS builds still need to
add `realpath(.)` to the `GDFONTPATH` as documented in the manual (or
pass absolute paths as `$fontfile`).

[1] <https://www.php.net/imagettftext>
[2] <libgd/libgd@2a921c8>

Closes GH-17366.

Author: cmb69

NEWS

@@ -35,6 +35,7 @@ PHP                                                                        NEWS
 - GD:
   . Fixed bug #68629 (Transparent artifacts when using imagerotate). (pierre,
     cmb)
+  . Fixed bug #64823 (ZTS GD fails to to find system TrueType font). (cmb)
 
 - Intl:
   . Bumped ICU requirement to ICU >= 57.1. (cmb)

ext/gd/gd.c

@@ -3374,18 +3374,6 @@ static void php_imagettftext_common(INTERNAL_FUNCTION_PARAMETERS, int mode)
 		}
 	}
 
-#ifdef VIRTUAL_DIR
-	{
-		char tmp_font_path[MAXPATHLEN];
-
-		if (!VCWD_REALPATH(fontname, tmp_font_path)) {
-			fontname = NULL;
-		}
-	}
-#endif /* VIRTUAL_DIR */
-
-	PHP_GD_CHECK_OPEN_BASEDIR(fontname, "Invalid font filename");
-
 	// libgd note: Those should return const char * ideally, but backward compatibility ..
 	if (EXT) {
 		error = gdImageStringFTEx(im, brect, col, fontname, ptsize, angle, x, y, str, &strex);