[PATCH v3] riscv: Fix a NULL pointer dereference in machine_kexec_prepare

[Tao Liu <ltao@redhat.com>]

A NULL pointer dereference issue is noticed in riscv's machine_kexec_prepare,
where image->segment[i].buf might be NULL and copied unchecked.

The NULL buf comes from security/integrity/ima/ima_kexec.c:
ima_add_kexec_buffer(), where kbuf is added by kexec_add_buffer(),
but kbuf.buffer is NULL.

Fix this by simply adding a check before copy.

Fixes: b7fb4d78a6ad ("RISC-V: use memcpy for kexec_file mode")
Acked-by: Baoquan He <bhe@redhat.com>
Acked-by: Pratyush Yadav <pratyush@kernel.org>
Signed-off-by: Tao Liu <ltao@redhat.com>
---

v3 -> v2: Add fixes tag; Replace "reference" to "dereference".
link to v2: https://lore.kernel.org/linux-riscv/20260627222602.23594-2-ltao@redhat.com/
link to v1: https://lore.kernel.org/linux-riscv/20260529032739.13264-2-ltao@redhat.com/

---
 arch/riscv/kernel/machine_kexec.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/riscv/kernel/machine_kexec.c b/arch/riscv/kernel/machine_kexec.c
index 2306ce3e5f22..afc68f6a4aa1 100644
--- a/arch/riscv/kernel/machine_kexec.c
+++ b/arch/riscv/kernel/machine_kexec.c
@@ -41,6 +41,13 @@ machine_kexec_prepare(struct kimage *image)
 		if (image->segment[i].memsz <= sizeof(fdt))
 			continue;
 
+		/*
+		 * Some segments (e.g. IMA) reserve space but have no buffer
+		 * loaded yet. Skip them as they cannot contain an FDT.
+		 */
+		if (image->segment[i].buf == NULL)
+			continue;
+
 		if (image->file_mode)
 			memcpy(&fdt, image->segment[i].buf, sizeof(fdt));
 		else if (copy_from_user(&fdt, image->segment[i].buf, sizeof(fdt)))
-- 
2.54.0