[PATCH -next v2 7/9] blk-iocost: fix UAF in ioc_pd_free

Li Nan
2022-11-30T13:01:04Z

Our test found the following problem in kernel 5.10, and the same problem
should exist in mainline:

BUG: KASAN: use-after-free in _raw_spin_lock_irqsave+0x71/0xe0
Write of size 4 at addr ffff8881432000e0 by task swapper/4/0
...
Call Trace:
<IRQ>
dump_stack+0x9c/0xd3
print_address_description.constprop.0+0x19/0x170
__kasan_report.cold+0x6c/0x84
kasan_report+0x3a/0x50
check_memory_region+0xfd/0x1f0
_raw_spin_lock_irqsave+0x71/0xe0
ioc_pd_free+0x9d/0x250
blkg_free.part.0+0x80/0x100
__blkg_release+0xf3/0x1c0
rcu_do_batch+0x292/0x700
rcu_core+0x270/0x2d0
__do_softirq+0xfd/0x402
</IRQ>
asm_call_irq_on_stack+0x12/0x20
do_softirq_own_stack+0x37/0x50
irq_exit_rcu+0x134/0x1a0
sysvec_apic_timer_interrupt+0x36/0x80
asm_sysvec_apic_timer_interrupt+0x12/0x20

Freed by task 57:
kfree+0xba/0x680
rq_qos_exit+0x5a/0x80
blk_cleanup_queue+0xce/0x1a0
virtblk_remove+0x77/0x130 [virtio_blk]
virtio_dev_remove+0x56/0xe0
__device_release_driver+0x2ba/0x450
device_release_driver+0x29/0x40
bus_remove_device+0x1d8/0x2c0
device_del+0x333/0x7e0
device_unregister+0x27/0x90
unregister_virtio_device+0x22/0x40
virtio_pci_remove+0x53/0xb0
pci_device_remove+0x7a/0x130
__device_release_driver+0x2ba/0x450
device_release_driver+0x29/0x40
pci_stop_bus_device+0xcf/0x100
pci_stop_and_remove_bus_device+0x16/0x20
disable_slot+0xa1/0x110
acpiphp_disable_and_eject_slot+0x35/0xe0
hotplug_event+0x1b8/0x3c0
acpiphp_hotplug_notify+0x37/0x70
acpi_device_hotplug+0xee/0x320
acpi_hotplug_work_fn+0x69/0x80
process_one_work+0x3c5/0x730
worker_thread+0x93/0x650
kthread+0x1ba/0x210
ret_from_fork+0x22/0x30

It happened as follow:

T1 T2 T3
//delete device
del_gendisk
bdi_unregister
bdi_remove_from_list
synchronize_rcu_expedited

//rmdir cgroup
blkcg_destroy_blkgs
blkg_destroy
percpu_ref_kill
blkg_release
call_rcu
rq_qos_exit
ioc_rqos_exit
kfree(ioc)
__blkg_release
blkg_free
blkg_free_workfn
pd_free_fn
ioc_pd_free
spin_lock_irqsave
->ioc is freed

Fix the problem by moving the operation on ioc in ioc_pd_free() to
ioc_pd_offline(), and just free resource in ioc_pd_free() like iolatency
and throttle.

Signed-off-by: Li Nan <linan122@huawei.com>
---
block/blk-iocost.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 2316ba93e7d6..710cf63a1643 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -2978,7 +2978,7 @@ static void ioc_pd_init(struct blkg_policy_data *pd)
spin_unlock_irqrestore(&ioc->lock, flags);
}

-static void ioc_pd_free(struct blkg_policy_data *pd)
+static void ioc_pd_offline(struct blkg_policy_data *pd)
{
struct ioc_gq *iocg = pd_to_iocg(pd);
struct ioc *ioc = iocg->ioc;
@@ -3002,6 +3002,12 @@ static void ioc_pd_free(struct blkg_policy_data *pd)

hrtimer_cancel(&iocg->waitq_timer);
}
+}
+
+static void ioc_pd_free(struct blkg_policy_data *pd)
+{
+ struct ioc_gq *iocg = pd_to_iocg(pd);
+
free_percpu(iocg->pcpu_stat);
kfree(iocg);
}
@@ -3488,6 +3494,7 @@ static struct blkcg_policy blkcg_policy_iocost = {
.cpd_free_fn = ioc_cpd_free,
.pd_alloc_fn = ioc_pd_alloc,
.pd_init_fn = ioc_pd_init,
+ .pd_offline_fn = ioc_pd_offline,
.pd_free_fn = ioc_pd_free,
.pd_stat_fn = ioc_pd_stat,
};
--
2.31.1