thermal/core: fix a UAF bug in __thermal_cooling_device_register()

When device_register() return failed, program will goto out_kfree_type
to release 'cdev->device' by put_device(). That will call thermal_release()
to free 'cdev'. But the follow-up processes access 'cdev' continually.
That trggers the UAF bug.

====================================================================
BUG: KASAN: use-after-free in __thermal_cooling_device_register+0x75b/0xa90
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
Call Trace:
 dump_stack_lvl+0xe2/0x152
 print_address_description.constprop.0+0x21/0x140
 ? __thermal_cooling_device_register+0x75b/0xa90
 kasan_report.cold+0x7f/0x11b
 ? __thermal_cooling_device_register+0x75b/0xa90
 __thermal_cooling_device_register+0x75b/0xa90
 ? memset+0x20/0x40
 ? __sanitizer_cov_trace_pc+0x1d/0x50
 ? __devres_alloc_node+0x130/0x180
 devm_thermal_of_cooling_device_register+0x67/0xf0
 max6650_probe.cold+0x557/0x6aa
......

Freed by task 258:
 kasan_save_stack+0x1b/0x40
 kasan_set_track+0x1c/0x30
 kasan_set_free_info+0x20/0x30
 __kasan_slab_free+0x109/0x140
 kfree+0x117/0x4c0
 thermal_release+0xa0/0x110
 device_release+0xa7/0x240
 kobject_put+0x1ce/0x540
 put_device+0x20/0x30
 __thermal_cooling_device_register+0x731/0xa90
 devm_thermal_of_cooling_device_register+0x67/0xf0
 max6650_probe.cold+0x557/0x6aa [max6650]

Do not use 'cdev' again after put_device() to fix the problem like doing
in thermal_zone_device_register().

[dlezcano]: as requested by Rafael, change the affectation into two statements.

Fixes: 5848376 ("thermal/drivers/core: Use a char pointer for the cooling device name")
Signed-off-by: Ziyang Xuan <[email protected]>
Reported-by: kernel test robot <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Daniel Lezcano <[email protected]>

Author: Ziyang Xuan

drivers/thermal/thermal_core.c

@@ -889,7 +889,7 @@ __thermal_cooling_device_register(struct device_node *np,
 {
 	struct thermal_cooling_device *cdev;
 	struct thermal_zone_device *pos = NULL;
-	int ret;
+	int id, ret;
 
 	if (!ops || !ops->get_max_state || !ops->get_cur_state ||
 	    !ops->set_cur_state)
@@ -903,6 +903,7 @@ __thermal_cooling_device_register(struct device_node *np,
 	if (ret < 0)
 		goto out_kfree_cdev;
 	cdev->id = ret;
+	id = ret;
 
 	ret = dev_set_name(&cdev->device, "cooling_device%d", cdev->id);
 	if (ret)
@@ -946,8 +947,9 @@ __thermal_cooling_device_register(struct device_node *np,
 out_kfree_type:
 	kfree(cdev->type);
 	put_device(&cdev->device);
+	cdev = NULL;
 out_ida_remove:
-	ida_simple_remove(&thermal_cdev_ida, cdev->id);
+	ida_simple_remove(&thermal_cdev_ida, id);
 out_kfree_cdev:
 	kfree(cdev);
 	return ERR_PTR(ret);