[PATCH 1/1] hw/arm: do not free machine->fdt in arm_load_dtb()

[Daniel Henrique Barboza]

At this moment, arm_load_dtb() can free machine->fdt when
binfo->dtb_filename is NULL. If there's no 'dtb_filename', 'fdt' will be
retrieved by binfo->get_dtb(). If get_dtb() returns machine->fdt, as is
the case of machvirt_dtb() from hw/arm/virt.c, fdt now has a pointer to
machine->fdt. And, in that case, the existing g_free(fdt) at the end of
arm_load_dtb() will make machine->fdt point to an invalid memory region.

After the command 'dumpdtb' were introduced a couple of releases ago,
running it with any ARM machine that uses arm_load_dtb() will crash
QEMU.

One alternative would be to mark machine->fdt = NULL when exiting
arm_load_dtb() when freeing the fdt. Another is to not free the fdt and,
instead, update machine->fdt with the new fdt generated. This will
enable dumpdtb for all ARM machines that uses arm_load_dtb(), regardless
of having 'dtb_filename' or not.

Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: qemu-arm@nongnu.org
Fixes: bf353ad55590f ("qmp/hmp, device_tree.c: introduce dumpdtb")
Reported-by: Markus Armbruster <armbru@redhat.com>i
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 hw/arm/boot.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/arm/boot.c b/hw/arm/boot.c
index 50e5141116..9418cc3373 100644
--- a/hw/arm/boot.c
+++ b/hw/arm/boot.c
@@ -689,7 +689,8 @@ int arm_load_dtb(hwaddr addr, const struct arm_boot_info 
*binfo,
     qemu_register_reset_nosnapshotload(qemu_fdt_randomize_seeds,
                                        rom_ptr_for_as(as, addr, size));
 
-    g_free(fdt);
+    /* Set ms->fdt for 'dumpdtb' QMP/HMP command */
+    ms->fdt = fdt;
 
     return size;
 
-- 
2.39.2