[xen staging] libfdt: fix UBSAN null pointer in fdt_property()

[patchbot@xxxxxxx]

commit be18ad502e5d4f9248e1f020d3e0d55a7b9ea986
Author:     Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
AuthorDate: Wed Jun 17 09:20:51 2026 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Jun 17 09:20:51 2026 +0200

    libfdt: fix UBSAN null pointer in fdt_property()
    
    fdt_property() unconditionally calls memcpy(ptr, val, len) even when
    len is zero and val is NULL.  This is a legitimate calling convention
    for adding empty FDT properties such as "interrupt-controller", which
    carry no payload.
    
    However, compilers that treat memcpy as nonnull on its pointer arguments
    will fire UBSAN before observing that len is zero.
    
    Guard the memcpy() with a check on len so it is skipped entirely when
    there is no payload to copy, bringing the code in line with the
    nonnull contract.
    
    Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
    Signed-off-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
    Origin: git://git.kernel.org/pub/scm/utils/dtc/dtc.git f57e7df35df4
    
    Fixes: f0ea06558068 ("libfdt: add version 1.3.0")
    Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
    Reviewed-by: Baptiste Le Duc <baptiste.le-duc@xxxxxxxxxx>
    Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
    Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
 xen/common/libfdt/fdt_sw.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/common/libfdt/fdt_sw.c b/xen/common/libfdt/fdt_sw.c
index 4c569ee7eb..96d4cf5713 100644
--- a/xen/common/libfdt/fdt_sw.c
+++ b/xen/common/libfdt/fdt_sw.c
@@ -330,7 +330,8 @@ int fdt_property(void *fdt, const char *name, const void 
*val, int len)
        ret = fdt_property_placeholder(fdt, name, len, &ptr);
        if (ret)
                return ret;
-       memcpy(ptr, val, len);
+       if (len)
+               memcpy(ptr, val, len);
        return 0;
 }
 
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