[PATCH RFC] block: fix use after free for bd_holder_dir/slave_dir

[Yu Kuai]

From: Yu Kuai <yukuai3@xxxxxxxxxx>

Our test report a following uaf:

==================================================================
BUG: KASAN: use-after-free in sysfs_remove_link+0x23/0x60
Read of size 8 at addr ffff888117398db0 by task dmsetup/1097

CPU: 12 PID: 1097 Comm: dmsetup Not tainted 6.0.0-next-20221007-00011-gf46c8956
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-4
Call Trace:
 <TASK>
 ? dump_stack_lvl+0x73/0x9f
 ? print_report+0x249/0x746
 ? __virt_addr_valid+0xd4/0x200
 ? sysfs_remove_link+0x23/0x60
 ? kasan_report+0xc0/0x120
 ? sysfs_remove_link+0x23/0x60
 ? __asan_load8+0x74/0x110
 ? sysfs_remove_link+0x23/0x60
 ? __unlink_disk_holder.isra.0+0x2f/0x80
 ? bd_unlink_disk_holder+0xd2/0x1c0
 ? dm_put_table_device+0xf1/0x250
 ? dm_put_device+0x14f/0x230
 ? linear_dtr+0x34/0x50
 ? dm_table_destroy+0x7b/0x280
 ? table_load+0x34a/0x710
 ? list_devices+0x4c0/0x4c0
 ? kvmalloc_node+0x7d/0x160
 ? __kmalloc_node+0x185/0x2b0
 ? ctl_ioctl+0x388/0x7b0
 ? list_devices+0x4c0/0x4c0
 ? free_params+0x50/0x50
 ? do_vfs_ioctl+0x931/0x10d0
 ? tick_program_event+0x65/0xd0
 ? __kasan_check_read+0x1d/0x30
 ? __fget_light+0xc2/0x370
 ? dm_ctl_ioctl+0x12/0x20
 ? __x64_sys_ioctl+0xd5/0x150
 ? do_syscall_64+0x35/0x80
 ? entry_SYSCALL_64_after_hwframe+0x63/0xcd
 </TASK>

Allocated by task 1097:
 kasan_save_stack+0x26/0x60
 kasan_set_track+0x29/0x40
 kasan_save_alloc_info+0x1f/0x40
 __kasan_kmalloc+0xcb/0xe0
 kmalloc_trace+0x7e/0x150
 kobject_create_and_add+0x3d/0xc0
 device_add_disk+0x429/0x7e0
 dm_setup_md_queue+0x15b/0x240
 table_load+0x469/0x710
 ctl_ioctl+0x388/0x7b0
 dm_ctl_ioctl+0x12/0x20
 __x64_sys_ioctl+0xd5/0x150
 do_syscall_64+0x35/0x80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 1097:
 kasan_save_stack+0x26/0x60
 kasan_set_track+0x29/0x40
 kasan_save_free_info+0x32/0x60
 __kasan_slab_free+0x172/0x2c0
 __kmem_cache_free+0x11c/0x560
 kfree+0xd3/0x240
 dynamic_kobj_release+0x1e/0x60
 kobject_put+0x192/0x410
 device_add_disk+0x535/0x7e0
 dm_setup_md_queue+0x15b/0x240
 table_load+0x469/0x710
 ctl_ioctl+0x388/0x7b0
 dm_ctl_ioctl+0x12/0x20
 __x64_sys_ioctl+0xd5/0x150
 do_syscall_64+0x35/0x80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

This problem is very easy to reporduce by injecting failure while creating
dm, and root cause is that lifetime of bd_holder_dir/slave_dir is
problematic:

1) device alloc
alloc_disk_node
 kzalloc_node			-> gendisk
 disk->part0 = bdev_alloc	-> part0
 device_initialize
  kobject_init()		-> part0->bd_device

2) device create
device_add_disk
 device_add
  kobject_add			-> part0->bd_device
 kobject_create_and_add		-> part0->bd_holder_dir
 kobject_create_and_add		-> gendisk->slave_dir

3) device remove
del_gendisk
 kobject_put			-> part0->bd_holder_dir
 kobject_put			-> gendisk->slave_dir
 device_del
  kobject_del			-> part0->bd_device

4) device free
disk_release
 iput
  bdev_free_inode
   kfree			-> gendisk
   kmem_cache_free		-> part0

bd_holder_dir and slave_dir is allocated in step 2), and freed in steup
3), while they are still accessible before step 4).

This patch delay the kobject destruction to disk_release/part_release to
fix the problem.

Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 block/genhd.c           | 7 ++++---
 block/partitions/core.c | 3 ++-
 drivers/base/core.c     | 1 -
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 514395361d7c..7ebd085d3a3f 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -615,9 +615,6 @@ void del_gendisk(struct gendisk *disk)
 
 	blk_unregister_queue(disk);
 
-	kobject_put(disk->part0->bd_holder_dir);
-	kobject_put(disk->slave_dir);
-
 	part_stat_set_all(disk->part0, 0);
 	disk->part0->bd_stamp = 0;
 	if (!sysfs_deprecated)
@@ -1139,6 +1136,10 @@ static void disk_release(struct device *dev)
 	might_sleep();
 	WARN_ON_ONCE(disk_live(disk));
 
+	kobject_put(disk->part0->bd_holder_dir);
+	kobject_put(disk->slave_dir);
+	kobject_del(&dev->kobj);
+
 	/*
 	 * To undo the all initialization from blk_mq_init_allocated_queue in
 	 * case of a probe failure where add_disk is never called we have to
diff --git a/block/partitions/core.c b/block/partitions/core.c
index b8112f52d388..b86a66198cc8 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -250,6 +250,8 @@ static const struct attribute_group *part_attr_groups[] = {
 
 static void part_release(struct device *dev)
 {
+	kobject_put(dev_to_bdev(dev)->bd_holder_dir);
+	kobject_del(&dev->kobj);
 	put_disk(dev_to_bdev(dev)->bd_disk);
 	iput(dev_to_bdev(dev)->bd_inode);
 }
@@ -279,7 +281,6 @@ static void delete_partition(struct block_device *part)
 	__invalidate_device(part, true);
 
 	xa_erase(&part->bd_disk->part_tbl, part->bd_partno);
-	kobject_put(part->bd_holder_dir);
 	device_del(&part->bd_device);
 
 	/*
diff --git a/drivers/base/core.c b/drivers/base/core.c
index d02501933467..d2ff3d2a8710 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -3712,7 +3712,6 @@ void device_del(struct device *dev)
 					     BUS_NOTIFY_REMOVED_DEVICE, dev);
 	kobject_uevent(&dev->kobj, KOBJ_REMOVE);
 	glue_dir = get_glue_dir(dev);
-	kobject_del(&dev->kobj);
 	cleanup_glue_dir(dev, glue_dir);
 	memalloc_noio_restore(noio_flag);
 	put_device(parent);
-- 
2.31.1