expat: fix CVE-2026-56410

These patches apply the upstream fixes shown in [1] and [2], as
referenced by [3].

[1] deeb97f7c8
[2] cee20e91bf
[3] https://nvd.nist.gov/vuln/detail/CVE-2026-56410

(From OE-Core rev: 51d1871b3551deddd9f5fac85fdcd4b2793b94f0)

Signed-off-by: Deepak Rathore <deeratho@cisco.com>
Signed-off-by: Fabien Thomas <fabien.thomas@smile.fr>
Signed-off-by: Paul Barker <paul@pbarker.dev>

meta/recipes-core/expat/expat/CVE-2026-56410_p1.patch

@@ -0,0 +1,46 @@
+From b454931c42290c9f0faf2a01f9634d82db636bac Mon Sep 17 00:00:00 2001
+From: netliomax25-code <netliomax25@gmail.com>
+Date: Fri, 29 May 2026 17:51:25 +0530
+Subject: [PATCH 06/17] xmlwf: protect resolveSystemId from integer overflow
+
+CVE: CVE-2026-56410
+Upstream-Status: Backport [https://github.com/libexpat/libexpat/commit/deeb97f7c88d17a16b0ea2521a13733abc283347]
+
+Backport Changes:
+- Adapt the allocation hunk to Scarthgap 2.6.4's explicit cast and
+  include stdint.h so SIZE_MAX is available.
+
+(cherry picked from commit deeb97f7c88d17a16b0ea2521a13733abc283347)
+Signed-off-by: Deepak Rathore <deeratho@cisco.com>
+---
+ expat/xmlwf/xmlfile.c | 10 ++++++++--
+ 1 file changed, 8 insertions(+), 2 deletions(-)
+
+diff --git a/expat/xmlwf/xmlfile.c b/expat/xmlwf/xmlfile.c
+index 9c4f7f8d..ad691b12 100644
+--- a/expat/xmlwf/xmlfile.c
++++ b/expat/xmlwf/xmlfile.c
+@@ -41,6 +41,7 @@
+ #include "expat_config.h"
+ 
+ #include <stdio.h>
++#include <stdint.h>
+ #include <stdlib.h>
+ #include <stddef.h>
+ #include <string.h>
+@@ -130,8 +131,13 @@ resolveSystemId(const XML_Char *base, const XML_Char *systemId,
+ #endif
+   )
+     return systemId;
+-  *toFree = (XML_Char *)malloc((tcslen(base) + tcslen(systemId) + 2)
+-                               * sizeof(XML_Char));
++  const size_t charsRequired = tcslen(base) + tcslen(systemId) + 2;
++
++  /* Detect and prevent integer overflow */
++  if (charsRequired > SIZE_MAX / sizeof(XML_Char))
++    return systemId;
++
++  *toFree = malloc(charsRequired * sizeof(XML_Char));
+   if (! *toFree)
+     return systemId;
+   tcscpy(*toFree, base);

meta/recipes-core/expat/expat/CVE-2026-56410_p2.patch

@@ -0,0 +1,39 @@
+From 7e6230212ddc4ea74115218fdbe5717e8e1c0f2b Mon Sep 17 00:00:00 2001
+From: netliomax25-code <netliomax25@gmail.com>
+Date: Sat, 30 May 2026 11:28:51 +0530
+Subject: [PATCH 07/17] xmlwf: guard each operator in resolveSystemId length
+ sum
+
+CVE: CVE-2026-56410
+Upstream-Status: Backport [https://github.com/libexpat/libexpat/commit/cee20e91bf14dc7f6d2fc48f0d70d86b2dc3afea]
+
+(cherry picked from commit cee20e91bf14dc7f6d2fc48f0d70d86b2dc3afea)
+Signed-off-by: Deepak Rathore <deeratho@cisco.com>
+---
+ expat/xmlwf/xmlfile.c | 12 ++++++++++--
+ 1 file changed, 10 insertions(+), 2 deletions(-)
+
+diff --git a/expat/xmlwf/xmlfile.c b/expat/xmlwf/xmlfile.c
+index ad691b12..4d2e3220 100644
+--- a/expat/xmlwf/xmlfile.c
++++ b/expat/xmlwf/xmlfile.c
+@@ -131,9 +131,17 @@ resolveSystemId(const XML_Char *base, const XML_Char *systemId,
+ #endif
+   )
+     return systemId;
+-  const size_t charsRequired = tcslen(base) + tcslen(systemId) + 2;
++  const size_t baseLen = tcslen(base);
++  const size_t systemIdLen = tcslen(systemId);
+ 
+-  /* Detect and prevent integer overflow */
++  /* Detect and prevent integer overflow in the addition (without risking
++     underflow) */
++  if (baseLen > SIZE_MAX - systemIdLen || baseLen > SIZE_MAX - systemIdLen - 2)
++    return systemId;
++
++  const size_t charsRequired = baseLen + systemIdLen + 2;
++
++  /* Detect and prevent integer overflow in the multiplication */
+   if (charsRequired > SIZE_MAX / sizeof(XML_Char))
+     return systemId;
+ 

meta/recipes-core/expat/expat_2.6.4.bb

@@ -66,6 +66,8 @@ SRC_URI = "${GITHUB_BASE_URI}/download/R_${VERSION_TAG}/expat-${PV}.tar.bz2  \
            file://CVE-2026-56408.patch;striplevel=2 \
            file://CVE-2026-56404.patch;striplevel=2 \
            file://CVE-2026-56405.patch;striplevel=2 \
+           file://CVE-2026-56410_p1.patch;striplevel=2 \
+           file://CVE-2026-56410_p2.patch;striplevel=2 \
            "
 
 GITHUB_BASE_URI = "https://github.com/libexpat/libexpat/releases/"