Fix #77391: 1bpp BMPs may fail to be loaded

We port the upstream fix[1].

[1] <libgd/libgd@d085913>

NEWS

@@ -2,6 +2,9 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? 2019, PHP 7.2.15
 
+- GD:
+  . Fixed bug #77391 (1bpp BMPs may fail to be loaded). (Romain Déoux, cmb)
+
 - Sockets:
   . Fixed bug #76839 (socket_recvfrom may return an invalid 'from' address
     on MacOS). (Michael Meyer)

ext/gd/libgd/gd_bmp.c

@@ -813,8 +813,8 @@ static int bmp_read_1bit(gdImagePtr im, gdIOCtxPtr infile, bmp_info_t *info, bmp
 		}
 	}
 
-	/* The line must be divisible by 4, else its padded with NULLs */
-	padding = ((int)ceil(0.1 * info->width)) % 4;
+	/* The line must be aligned on a 32 bits word, else it is padded with zeros */
+	padding = (info->width + 7) / 8 % 4;
 	if (padding) {
 		padding = 4 - padding;
 	}

ext/gd/tests/bug77391.phpt

@@ -0,0 +1,15 @@
+--TEST--
+Bug #77391 (1bpp BMPs may fail to be loaded)
+--SKIPIF--
+<?php
+if (!extension_loaded('gd')) die('skip gd extension not available');
+if (!GD_BUNDLED && version_compare(GD_VERSION, '2.2.5', '<=')) die('skip upstream not yet fixed');
+?>
+--FILE--
+<?php
+var_dump(imagecreatefrombmp(__DIR__ . '/bug77391.bmp'));
+?>
+===DONE===
+--EXPECTF--
+resource(%d) of type (gd)
+===DONE===