mtd: core: Fix refcount error in del_mtd_device()

In the Linux kernel, the following vulnerability has been resolved:

mtd: core: Fix refcount error in del_mtd_device()

del_mtd_device() will call of_node_put() to mtd_get_of_node(mtd), which

is mtd->dev.of_node. However, memset(&mtd->dev, 0) is called before

of_node_put(). As the result, of_node_put() won't do anything in

del_mtd_device(), and causes the refcount leak.

del_mtd_device()

memset(&mtd->dev, 0, sizeof(mtd->dev) # clear mtd->dev

of_node_put()

mtd_get_of_node(mtd) # mtd->dev is cleared, can't locate of_node

# of_node_put(NULL) won't do anything

Fix the error by caching the pointer of the device_node.

OF: ERROR: memory leak, expected refcount 1 instead of 2,

of_node_get()/of_node_put() unbalanced - destroy cset entry: attach

overlay node /spi/spi-sram@0

CPU: 3 PID: 275 Comm: python3 Tainted: G N 6.1.0-rc3+ #54

0d8a1edddf51f172ff5226989a7565c6313b08e2

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS

rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014

Call Trace:

<TASK>

dump_stack_lvl+0x67/0x83

kobject_get+0x155/0x160

of_node_get+0x1f/0x30

of_fwnode_get+0x43/0x70

fwnode_handle_get+0x54/0x80

fwnode_get_nth_parent+0xc9/0xe0

fwnode_full_name_string+0x3f/0xa0

device_node_string+0x30f/0x750

pointer+0x598/0x7a0

vsnprintf+0x62d/0x9b0

...

cfs_overlay_release+0x30/0x90

config_item_release+0xbe/0x1a0

config_item_put+0x5e/0x80

configfs_rmdir+0x3bd/0x540

vfs_rmdir+0x18c/0x320

do_rmdir+0x198/0x330

__x64_sys_rmdir+0x2c/0x40

do_syscall_64+0x37/0x90

entry_SYSCALL_64_after_hwframe+0x63/0xcd

[<[email protected]>: Light reword of the commit log]