expat: fix CVE-2026-56409

This patch applies the upstream fix shown in [1] as referenced by [2].

[1] 61f7cdda22
[2] https://nvd.nist.gov/vuln/detail/CVE-2026-56409

(From OE-Core rev: 6e0669fdbf661569083b7fe479bf829e6e476f72)

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-2026-56409.patch

@@ -0,0 +1,51 @@
+From 174ce18f2a283be634d830a5259bd07142635fe8 Mon Sep 17 00:00:00 2001
+From: netliomax25-code <netliomax25@gmail.com>
+Date: Mon, 1 Jun 2026 11:53:19 +0530
+Subject: [PATCH 10/17] xmlwf: protect output path join from integer overflow
+
+CVE: CVE-2026-56409
+Upstream-Status: Backport [https://github.com/libexpat/libexpat/commit/61f7cdda22546c4bee38dd2d3fa3d6e4aa64d33e]
+
+Backport Changes:
+- Adapt the allocation hunk to the explicit XML_Char cast used by
+  Scarthgap 2.6.4; overflow checks are unchanged.
+
+(cherry picked from commit 61f7cdda22546c4bee38dd2d3fa3d6e4aa64d33e)
+Signed-off-by: Deepak Rathore <deeratho@cisco.com>
+---
+ expat/xmlwf/xmlwf.c | 22 ++++++++++++++++++++--
+ 1 file changed, 20 insertions(+), 2 deletions(-)
+
+diff --git a/expat/xmlwf/xmlwf.c b/expat/xmlwf/xmlwf.c
+index 7bbdb303..bd5f68a4 100644
+--- a/expat/xmlwf/xmlwf.c
++++ b/expat/xmlwf/xmlwf.c
+@@ -1240,8 +1240,26 @@ tmain(int argc, XML_Char **argv) {
+         }
+ #endif
+       }
+-      outName = (XML_Char *)malloc((tcslen(outputDir) + tcslen(file) + 2)
+-                                   * sizeof(XML_Char));
++      const size_t outputDirLen = tcslen(outputDir);
++      const size_t fileLen = tcslen(file);
++
++      /* Detect and prevent integer overflow in the addition (without
++         risking underflow) and the multiplication, mirroring the guards
++         in xcsdup() and resolveSystemId() */
++      if (outputDirLen > SIZE_MAX - fileLen
++          || outputDirLen > SIZE_MAX - fileLen - 2) {
++        tperror(T("Could not allocate memory"));
++        exit(XMLWF_EXIT_INTERNAL_ERROR);
++      }
++
++      const size_t charsRequired = outputDirLen + fileLen + 2;
++
++      if (charsRequired > SIZE_MAX / sizeof(XML_Char)) {
++        tperror(T("Could not allocate memory"));
++        exit(XMLWF_EXIT_INTERNAL_ERROR);
++      }
++
++      outName = malloc(charsRequired * sizeof(XML_Char));
+       if (! outName) {
+         tperror(T("Could not allocate memory"));
+         exit(XMLWF_EXIT_INTERNAL_ERROR);

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

@@ -70,6 +70,7 @@ SRC_URI = "${GITHUB_BASE_URI}/download/R_${VERSION_TAG}/expat-${PV}.tar.bz2  \
            file://CVE-2026-56410_p2.patch;striplevel=2 \
            file://CVE-2026-56406-dependent.patch;striplevel=2 \
            file://CVE-2026-56406.patch;striplevel=2 \
+           file://CVE-2026-56409.patch;striplevel=2 \
            "
 
 GITHUB_BASE_URI = "https://github.com/libexpat/libexpat/releases/"