gnu: cairo: Reintroduce security patches [security fixes].

Two patches were accidentally removed in commit
f94cdc86f644984ca83164d40b17e7eed6e22091.

* gnu/packages/patches/cairo-CVE-2018-19876.patch,
gnu/packages/patches/cairo-CVE-2020-35492.patch: New files.
* gnu/local.mk (dist_patch_DATA): Add them.
* gnu/packages/gtk.scm (cairo)[patches]: Apply them.

1 files changed, 49 insertions, 0 deletions

diff --git a/gnu/packages/patches/cairo-CVE-2020-35492.patch b/gnu/packages/patches/cairo-CVE-2020-35492.patch
new file mode 100644
index 0000000000..e8b90fa5c5
--- /dev/null
+++ b/gnu/packages/patches/cairo-CVE-2020-35492.patch
@@ -0,0 +1,49 @@
+Copied from Debian.
+
+From 03a820b173ed1fdef6ff14b4468f5dbc02ff59be Mon Sep 17 00:00:00 2001
+From: Heiko Lewin <heiko.lewin@worldiety.de>
+Date: Tue, 15 Dec 2020 16:48:19 +0100
+Subject: [PATCH] Fix mask usage in image-compositor
+
+[trimmed test case, since not used in Debian build]
+
+---
+ src/cairo-image-compositor.c                |   8 ++--
+
+--- cairo-1.16.0.orig/src/cairo-image-compositor.c
++++ cairo-1.16.0/src/cairo-image-compositor.c
+@@ -2601,14 +2601,14 @@ _inplace_src_spans (void *abstract_rende
+ 		    unsigned num_spans)
+ {
+     cairo_image_span_renderer_t *r = abstract_renderer;
+-    uint8_t *m;
++    uint8_t *m, *base = (uint8_t*)pixman_image_get_data(r->mask);
+     int x0;
+ 
+     if (num_spans == 0)
+ 	return CAIRO_STATUS_SUCCESS;
+ 
+     x0 = spans[0].x;
+-    m = r->_buf;
++    m = base;
+     do {
+ 	int len = spans[1].x - spans[0].x;
+ 	if (len >= r->u.composite.run_length && spans[0].coverage == 0xff) {
+@@ -2646,7 +2646,7 @@ _inplace_src_spans (void *abstract_rende
+ 				      spans[0].x, y,
+ 				      spans[1].x - spans[0].x, h);
+ 
+-	    m = r->_buf;
++	    m = base;
+ 	    x0 = spans[1].x;
+ 	} else if (spans[0].coverage == 0x0) {
+ 	    if (spans[0].x != x0) {
+@@ -2675,7 +2675,7 @@ _inplace_src_spans (void *abstract_rende
+ #endif
+ 	    }
+ 
+-	    m = r->_buf;
++	    m = base;
+ 	    x0 = spans[1].x;
+ 	} else {
+ 	    *m++ = spans[0].coverage;