[PATCH 6.9 275/374] null_blk: fix null-ptr-dereference while configuring power and submit_queues

Greg Kroah-Hartman
2024-06-06T14:11:03Z

From: Yu Kuai <yukuai3@huawei.com>

[ Upstream commit a2db328b0839312c169eb42746ec46fc1ab53ed2 ]

Writing 'power' and 'submit_queues' concurrently will trigger kernel
panic:

Test script:

modprobe null_blk nr_devices=0
mkdir -p /sys/kernel/config/nullb/nullb0
while true; do echo 1 > submit_queues; echo 4 > submit_queues; done &
while true; do echo 1 > power; echo 0 > power; done

Test result:

BUG: kernel NULL pointer dereference, address: 0000000000000148
Oops: 0000 [#1] PREEMPT SMP
RIP: 0010:__lock_acquire+0x41d/0x28f0
Call Trace:
<TASK>
lock_acquire+0x121/0x450
down_write+0x5f/0x1d0
simple_recursive_removal+0x12f/0x5c0
blk_mq_debugfs_unregister_hctxs+0x7c/0x100
blk_mq_update_nr_hw_queues+0x4a3/0x720
nullb_update_nr_hw_queues+0x71/0xf0 [null_blk]
nullb_device_submit_queues_store+0x79/0xf0 [null_blk]
configfs_write_iter+0x119/0x1e0
vfs_write+0x326/0x730
ksys_write+0x74/0x150

This is because del_gendisk() can concurrent with
blk_mq_update_nr_hw_queues():

nullb_device_power_store nullb_apply_submit_queues
null_del_dev
del_gendisk
nullb_update_nr_hw_queues
if (!dev->nullb)
// still set while gendisk is deleted
return 0
blk_mq_update_nr_hw_queues
dev->nullb = NULL

Fix this problem by resuing the global mutex to protect
nullb_device_power_store() and nullb_update_nr_hw_queues() from configfs.

Fixes: 45919fbfe1c4 ("null_blk: Enable modifying 'submit_queues' after an instance has been configured")
Reported-and-tested-by: Yi Zhang <yi.zhang@redhat.com>
Closes: https://lore.kernel.org/all/CAHj4cs9LgsHLnjg8z06LQ3Pr5cax-+Ps+xT7AP7TPnEjStuwZA@mail.gmail.com/
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Link: https://lore.kernel.org/r/20240523153934.1937851-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/block/null_blk/main.c | 40 +++++++++++++++++++++++------------
1 file changed, 26 insertions(+), 14 deletions(-)

diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 14ffda1ffe6c3..3b3fd093b0044 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -404,13 +404,25 @@ static int nullb_update_nr_hw_queues(struct nullb_device *dev,
static int nullb_apply_submit_queues(struct nullb_device *dev,
unsigned int submit_queues)
{
- return nullb_update_nr_hw_queues(dev, submit_queues, dev->poll_queues);
+ int ret;
+
+ mutex_lock(&lock);
+ ret = nullb_update_nr_hw_queues(dev, submit_queues, dev->poll_queues);
+ mutex_unlock(&lock);
+
+ return ret;
}

static int nullb_apply_poll_queues(struct nullb_device *dev,
unsigned int poll_queues)
{
- return nullb_update_nr_hw_queues(dev, dev->submit_queues, poll_queues);
+ int ret;
+
+ mutex_lock(&lock);
+ ret = nullb_update_nr_hw_queues(dev, dev->submit_queues, poll_queues);
+ mutex_unlock(&lock);
+
+ return ret;
}

NULLB_DEVICE_ATTR(size, ulong, NULL);
@@ -457,28 +469,31 @@ static ssize_t nullb_device_power_store(struct config_item *item,
if (ret < 0)
return ret;

+ ret = count;
+ mutex_lock(&lock);
if (!dev->power && newp) {
if (test_and_set_bit(NULLB_DEV_FL_UP, &dev->flags))
- return count;
+ goto out;
+
ret = null_add_dev(dev);
if (ret) {
clear_bit(NULLB_DEV_FL_UP, &dev->flags);
- return ret;
+ goto out;
}

set_bit(NULLB_DEV_FL_CONFIGURED, &dev->flags);
dev->power = newp;
} else if (dev->power && !newp) {
if (test_and_clear_bit(NULLB_DEV_FL_UP, &dev->flags)) {
- mutex_lock(&lock);
dev->power = newp;
null_del_dev(dev->nullb);
- mutex_unlock(&lock);
}
clear_bit(NULLB_DEV_FL_CONFIGURED, &dev->flags);
}

- return count;
+out:
+ mutex_unlock(&lock);
+ return ret;
}

CONFIGFS_ATTR(nullb_device_, power);
@@ -1918,15 +1933,12 @@ static int null_add_dev(struct nullb_device *dev)
nullb->q->queuedata = nullb;
blk_queue_flag_set(QUEUE_FLAG_NONROT, nullb->q);

- mutex_lock(&lock);
rv = ida_alloc(&nullb_indexes, GFP_KERNEL);
- if (rv < 0) {
- mutex_unlock(&lock);
+ if (rv < 0)
goto out_cleanup_disk;
- }
+
nullb->index = rv;
dev->index = rv;
- mutex_unlock(&lock);

if (config_item_name(&dev->group.cg_item)) {
/* Use configfs dir name as the device name */
@@ -1955,9 +1967,7 @@ static int null_add_dev(struct nullb_device *dev)
if (rv)
goto out_ida_free;

- mutex_lock(&lock);
list_add_tail(&nullb->list, &nullb_list);
- mutex_unlock(&lock);

pr_info("disk %s created\n", nullb->disk_name);

@@ -2006,7 +2016,9 @@ static int null_create_dev(void)
if (!dev)
return -ENOMEM;

+ mutex_lock(&lock);
ret = null_add_dev(dev);
+ mutex_unlock(&lock);
if (ret) {
null_free_dev(dev);
return ret;
--
2.43.0