[OE-core][wrynose][PATCH v2 02/10] expat: fix CVE-2026-56408

["Deepak Rathore -X (deeratho - E INFOCHIPS PRIVATE LIMITED at Cisco)" <deeratho@cisco.com>]

From: Deepak Rathore <deeratho@cisco.com>

This patch applies the upstream fix shown in [1] as referenced by [2].
The fix is adapted to the existing Expat 2.7.5 copyString implementation.

[1] https://github.com/libexpat/libexpat/commit/16e2efd867ea8567ffa012210b52ef5918e20817
[2] https://nvd.nist.gov/vuln/detail/CVE-2026-56408

Signed-off-by: Deepak Rathore <deeratho@cisco.com>
---
- Changes from v1 to v2: Refresh the patch on top of
latest wrynose branch merged commits.
 .../expat/expat/CVE-2026-56408.patch          | 36 +++++++++++++++++++
 meta/recipes-core/expat/expat_2.7.5.bb        |  1 +
 2 files changed, 37 insertions(+)
 create mode 100644 meta/recipes-core/expat/expat/CVE-2026-56408.patch

diff --git a/meta/recipes-core/expat/expat/CVE-2026-56408.patch b/meta/recipes-core/expat/expat/CVE-2026-56408.patch
new file mode 100644
index 0000000000..b8c43636cc
--- /dev/null
+++ b/meta/recipes-core/expat/expat/CVE-2026-56408.patch
@@ -0,0 +1,36 @@
+From b0cf9e9b0f5dfdd938148931a4605a0fd6b917a7 Mon Sep 17 00:00:00 2001
+From: Sebastian Pipping <sebastian@pipping.org>
+Date: Thu, 23 Apr 2026 10:31:45 +0200
+Subject: [PATCH] lib: Waterproof `copyString` from integer overflow
+
+CVE: CVE-2026-56408
+Upstream-Status: Backport [https://github.com/libexpat/libexpat/commit/16e2efd867ea8567ffa012210b52ef5918e20817]
+
+Backport Changes:
+- Adapt the fix to Expat 2.7.5, which calculates charsRequired using
+  an existing loop instead of xcslen. The upstream string helper
+  refactoring is not required for the overflow guard.
+
+(cherry picked from commit 16e2efd867ea8567ffa012210b52ef5918e20817)
+Signed-off-by: Deepak Rathore <deeratho@cisco.com>
+---
+ expat/lib/xmlparse.c | 4 ++++
+ 1 file changed, 4 insertions(+)
+
+diff --git a/expat/lib/xmlparse.c b/expat/lib/xmlparse.c
+index e441ff7f..4ff5e33b 100644
+--- a/expat/lib/xmlparse.c
++++ b/expat/lib/xmlparse.c
+@@ -8505,6 +8505,10 @@ copyString(const XML_Char *s, XML_Parser parser) {
+   /* Include the terminator */
+   charsRequired++;
+ 
++  /* Detect and prevent integer overflow */
++  if (charsRequired > SIZE_MAX / sizeof(XML_Char))
++    return NULL;
++
+   /* Now allocate space for the copy */
+   result = MALLOC(parser, charsRequired * sizeof(XML_Char));
+   if (result == NULL)
+-- 
+2.43.7
diff --git a/meta/recipes-core/expat/expat_2.7.5.bb b/meta/recipes-core/expat/expat_2.7.5.bb
index 423219c726..934cde4b1a 100644
--- a/meta/recipes-core/expat/expat_2.7.5.bb
+++ b/meta/recipes-core/expat/expat_2.7.5.bb
@@ -21,6 +21,7 @@ SRC_URI = "${GITHUB_BASE_URI}/download/R_${VERSION_TAG}/expat-${PV}.tar.bz2  \
            file://CVE-2026-41080-2.patch \
            file://CVE-2026-56403_p1.patch;striplevel=2 \
            file://CVE-2026-56403_p2.patch;striplevel=2 \
+           file://CVE-2026-56408.patch;striplevel=2 \
            "
 
 GITHUB_BASE_URI = "https://github.com/libexpat/libexpat/releases/"
-- 
2.35.6