A static Sashiko AI review identified a potential NULL pointer dereference
in kexec_extra_fdt_size_ppc64().

When get_reserved_memory_ranges() successfully returns 0 on platforms
without any reserved memory regions, the allocated 'rmem' pointer remains
NULL. Passing this unallocated pointer directly to
kexec_extra_fdt_size_ppc64() leads to a kernel panic when evaluating
'rmem->nr_ranges'.

Fix this by adding a defensive NULL pointer check at the beginning of
kexec_extra_fdt_size_ppc64(), returning 0 extra space immediately if
no reserved memory structure exists.

Cc: Sourabh Jain <redacted>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: stable@vger.kernel.org
Fixes: 0d3ff067331e ("powerpc/kexec_file: fix extra size calculation for kexec FDT")
Signed-off-by: Jinjie Ruan <redacted>
---
 arch/powerpc/kexec/file_load_64.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c
index 8c72e12ea44e..fdeedf102c38 100644
--- a/arch/powerpc/kexec/file_load_64.c
+++ b/arch/powerpc/kexec/file_load_64.c

@@ -649,6 +649,9 @@ unsigned int kexec_extra_fdt_size_ppc64(struct kimage *image, struct crash_mem *
 	struct device_node *dn;
 	unsigned int cpu_nodes = 0, extra_size = 0;
 
+	if (!rmem)
+		return 0;
+
 	// Budget some space for the password blob. There's already extra space
 	// for the key name
 	if (plpks_is_available())

-- 
2.34.1