[PATCH v2 1/1] hw/arm: do not free machine->fdt in arm_load_dtb()

[Daniel Henrique Barboza <danielhb413@gmail.com>]

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.

Let's enable all arm_load_dtb() callers to use dumpdtb properly. Instead
of freeing 'fdt', assign it back to ms->fdt.

Note that all current callers (sbsa-ref.c, virt.c, xlnx-versal-virt.c)
are assigning ms->fdt before arm_load_dtb() is called, regardless of
whether the user is inputting an external FDT via '-dtb'. To avoid
leaking the board FDT if '-dtb' is used (since we're assigning ms->fdt
in the end), free ms->fdt before load_device_tree().

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 | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/hw/arm/boot.c b/hw/arm/boot.c
index 50e5141116..de18c0a969 100644
--- a/hw/arm/boot.c
+++ b/hw/arm/boot.c
@@ -549,6 +549,13 @@ int arm_load_dtb(hwaddr addr, const struct arm_boot_info *binfo,
             goto fail;
         }
 
+        /*
+         * If we're here we won't be using the ms->fdt from the board.
+         * We'll assign a new ms->fdt at the end, so free it now to
+         * avoid leaking the board FDT.
+         */
+        g_free(ms->fdt);
+
         fdt = load_device_tree(filename, &size);
         if (!fdt) {
             fprintf(stderr, "Couldn't open dtb file %s\n", filename);
@@ -689,7 +696,8 @@ 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