libxml2: Fix CVE-2021-3518

There's a flaw in libxml2 in versions before 2.9.11. An attacker who is able to submit a crafted file to be processed by an application linked with libxml2 could trigger a use-after-free. The greatest impact from this flaw is to confidentiality, integrity, and availability.

Upstream-Status: Backport [from fedora:
https://bugzilla.redhat.com/show_bug.cgi?id=1954243]

Signed-off-by: Jasper Orschulko <jasper@fancydomain.eu>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

2 files changed, 113 insertions, 0 deletions

diff --git a/meta/recipes-core/libxml/libxml2/CVE-2021-3518.patch b/meta/recipes-core/libxml/libxml2/CVE-2021-3518.patch
new file mode 100644
index 0000000000..40d3debea1
--- /dev/null
+++ b/meta/recipes-core/libxml/libxml2/CVE-2021-3518.patch
@@ -0,0 +1,112 @@
+From ac82a514e16eb81b4506e2cba1a1ee45b9f025b5 Mon Sep 17 00:00:00 2001
+From: Nick Wellnhofer <wellnhofer@aevum.de>
+Date: Wed, 10 Jun 2020 16:34:52 +0200
+Subject: [PATCH 1/2] Don't recurse into xi:include children in
+ xmlXIncludeDoProcess
+
+Otherwise, nested xi:include nodes might result in a use-after-free
+if XML_PARSE_NOXINCNODE is specified.
+
+Found with libFuzzer and ASan.
+
+Upstream-Status: Backport [from fedora: https://bugzilla.redhat.com/show_bug.cgi?id=1954243]
+
+The upstream patch 752e5f71d7cea2ca5a7e7c0b8f72ed04ce654be4 has been modified,
+as to avoid unnecessary modifications to fallback files.
+
+CVE: CVE-2021-3518
+Signed-off-by: Jasper Orschulko <Jasper.Orschulko@iris-sensing.com>
+---
+ xinclude.c | 24 ++++++++++--------------
+ 1 file changed, 10 insertions(+), 14 deletions(-)
+
+diff --git a/xinclude.c b/xinclude.c
+index ba850fa5..f260c1a7 100644
+--- a/xinclude.c
++++ b/xinclude.c
+@@ -2392,21 +2392,19 @@ xmlXIncludeDoProcess(xmlXIncludeCtxtPtr ctxt, xmlDocPtr doc, xmlNodePtr tree) {
+      * First phase: lookup the elements in the document
+      */
+     cur = tree;
+-    if (xmlXIncludeTestNode(ctxt, cur) == 1)
+-	xmlXIncludePreProcessNode(ctxt, cur);
+     while ((cur != NULL) && (cur != tree->parent)) {
+ 	/* TODO: need to work on entities -> stack */
+-	if ((cur->children != NULL) &&
+-	    (cur->children->type != XML_ENTITY_DECL) &&
+-	    (cur->children->type != XML_XINCLUDE_START) &&
+-	    (cur->children->type != XML_XINCLUDE_END)) {
+-	    cur = cur->children;
+-	    if (xmlXIncludeTestNode(ctxt, cur))
+-		xmlXIncludePreProcessNode(ctxt, cur);
+-	} else if (cur->next != NULL) {
++        if (xmlXIncludeTestNode(ctxt, cur) == 1) {
++            xmlXIncludePreProcessNode(ctxt, cur);
++        } else if ((cur->children != NULL) &&
++                   (cur->children->type != XML_ENTITY_DECL) &&
++                   (cur->children->type != XML_XINCLUDE_START) &&
++                   (cur->children->type != XML_XINCLUDE_END)) {
++            cur = cur->children;
++            continue;
++        }
++	if (cur->next != NULL) {
+ 	    cur = cur->next;
+-	    if (xmlXIncludeTestNode(ctxt, cur))
+-		xmlXIncludePreProcessNode(ctxt, cur);
+ 	} else {
+ 	    if (cur == tree)
+ 	        break;
+@@ -2416,8 +2414,6 @@ xmlXIncludeDoProcess(xmlXIncludeCtxtPtr ctxt, xmlDocPtr doc, xmlNodePtr tree) {
+ 		    break; /* do */
+ 		if (cur->next != NULL) {
+ 		    cur = cur->next;
+-		    if (xmlXIncludeTestNode(ctxt, cur))
+-			xmlXIncludePreProcessNode(ctxt, cur);
+ 		    break; /* do */
+ 		}
+ 	    } while (cur != NULL);
+-- 
+2.32.0
+
+
+From 3ad5ac1e39e3cd42f838c1cd27ffd4e9b79e6121 Mon Sep 17 00:00:00 2001
+From: Nick Wellnhofer <wellnhofer@aevum.de>
+Date: Thu, 22 Apr 2021 19:26:28 +0200
+Subject: [PATCH 2/2] Fix user-after-free with `xmllint --xinclude --dropdtd`
+
+The --dropdtd option can leave dangling pointers in entity reference
+nodes. Make sure to skip these nodes when processing XIncludes.
+
+This also avoids scanning entity declarations and even modifying
+them inadvertently during XInclude processing.
+
+Move from a block list to an allow list approach to avoid descending
+into other node types that can't contain elements.
+
+Fixes #237.
+Upstream-Status: Backport
+CVE: CVE-2021-3518
+Signed-off-by: Jasper Orschulko <Jasper.Orschulko@iris-sensing.com>
+---
+ xinclude.c | 5 ++---
+ 1 file changed, 2 insertions(+), 3 deletions(-)
+
+diff --git a/xinclude.c b/xinclude.c
+index f260c1a7..d7648529 100644
+--- a/xinclude.c
++++ b/xinclude.c
+@@ -2397,9 +2397,8 @@ xmlXIncludeDoProcess(xmlXIncludeCtxtPtr ctxt, xmlDocPtr doc, xmlNodePtr tree) {
+         if (xmlXIncludeTestNode(ctxt, cur) == 1) {
+             xmlXIncludePreProcessNode(ctxt, cur);
+         } else if ((cur->children != NULL) &&
+-                   (cur->children->type != XML_ENTITY_DECL) &&
+-                   (cur->children->type != XML_XINCLUDE_START) &&
+-                   (cur->children->type != XML_XINCLUDE_END)) {
++                   ((cur->type == XML_DOCUMENT_NODE) ||
++                    (cur->type == XML_ELEMENT_NODE))) {
+             cur = cur->children;
+             continue;
+         }
+-- 
+2.32.0
+
diff --git a/meta/recipes-core/libxml/libxml2_2.9.10.bb b/meta/recipes-core/libxml/libxml2_2.9.10.bb
index 097613fb28..b5fb3e6315 100644
--- a/meta/recipes-core/libxml/libxml2_2.9.10.bb
+++ b/meta/recipes-core/libxml/libxml2_2.9.10.bb
@@ -25,6 +25,7 @@ SRC_URI = "http://www.xmlsoft.org/sources/libxml2-${PV}.tar.gz;name=libtar \
            file://CVE-2020-24977.patch \
            file://CVE-2021-3517.patch \
            file://CVE-2021-3537.patch \
+           file://CVE-2021-3518.patch \
            "
 
 SRC_URI[libtar.md5sum] = "10942a1dc23137a8aa07f0639cbfece5"