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

From: Ziyang Xuan
Date: Thu Oct 14 2021 - 04:47:59 EST


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().

Fixes: 584837618100 ("thermal/drivers/core: Use a char pointer for the cooling device name")
Signed-off-by: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx>
---
drivers/thermal/thermal_core.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
index 97ef9b040b84..ee7453944ccb 100644
--- a/drivers/thermal/thermal_core.c
+++ b/drivers/thermal/thermal_core.c
@@ -888,7 +888,7 @@ __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)
@@ -898,10 +898,10 @@ __thermal_cooling_device_register(struct device_node *np,
if (!cdev)
return ERR_PTR(-ENOMEM);

- ret = ida_simple_get(&thermal_cdev_ida, 0, 0, GFP_KERNEL);
- if (ret < 0)
+ id = ida_simple_get(&thermal_cdev_ida, 0, 0, GFP_KERNEL);
+ if (id < 0)
goto out_kfree_cdev;
- cdev->id = ret;
+ cdev->id = id;

cdev->type = kstrdup(type ? type : "", GFP_KERNEL);
if (!cdev->type) {
@@ -942,8 +942,9 @@ __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);
--
2.25.1