package/cairo: fix CVE-2019-6462

Add an upstream patch to fix CVE-2019-6462:

An issue was discovered in cairo 1.16.0. There is an infinite loop in
the function _arc_error_normalized in the file cairo-arc.c, related to
_arc_max_angle_for_tolerance_normalized.

Cc: Quentin Schulz <foss+buildroot@0leil.net>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/cairo/0003-_arc_max_angle_for_tolerance_normalized-fix-infinite.patch

@@ -0,0 +1,39 @@
+From ab2c5ee21e5f3d3ee4b3f67cfcd5811a4f99c3a0 Mon Sep 17 00:00:00 2001
+From: Heiko Lewin <hlewin@gmx.de>
+Date: Sun, 1 Aug 2021 11:16:03 +0000
+Subject: [PATCH] _arc_max_angle_for_tolerance_normalized: fix infinite loop
+
+[Retrieved from:
+https://gitlab.freedesktop.org/cairo/cairo/-/commit/ab2c5ee21e5f3d3ee4b3f67cfcd5811a4f99c3a0]
+Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
+---
+ src/cairo-arc.c | 4 +++-
+ 1 file changed, 3 insertions(+), 1 deletion(-)
+
+diff --git a/src/cairo-arc.c b/src/cairo-arc.c
+index 390397bae..1c891d1a0 100644
+--- a/src/cairo-arc.c
++++ b/src/cairo-arc.c
+@@ -90,16 +90,18 @@ _arc_max_angle_for_tolerance_normalized (double tolerance)
+ 	{ M_PI / 11.0,  9.81410988043554039085e-09 },
+     };
+     int table_size = ARRAY_LENGTH (table);
++    const int max_segments = 1000; /* this value is chosen arbitrarily. this gives an error of about 1.74909e-20 */
+ 
+     for (i = 0; i < table_size; i++)
+ 	if (table[i].error < tolerance)
+ 	    return table[i].angle;
+ 
+     ++i;
++
+     do {
+ 	angle = M_PI / i++;
+ 	error = _arc_error_normalized (angle);
+-    } while (error > tolerance);
++    } while (error > tolerance && i < max_segments);
+ 
+     return angle;
+ }
+-- 
+2.38.1
+

package/cairo/cairo.mk

@@ -14,6 +14,8 @@ CAIRO_INSTALL_STAGING = YES
 
 # 0002-ft-Use-FT_Done_MM_Var-instead-of-free-when-available-in-cairo_ft_apply_variation.patch
 CAIRO_IGNORE_CVES += CVE-2018-19876
+# 0003-_arc_max_angle_for_tolerance_normalized-fix-infinite.patch
+CAIRO_IGNORE_CVES += CVE-2019-6462
 
 CAIRO_CONF_ENV = LIBS="$(CAIRO_LIBS)"