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

[Yu Kuai]

Hi,

在 2022/10/17 19:36, Christoph Hellwig 写道:
> On Mon, Oct 17, 2022 at 05:24:20PM +0800, Yu Kuai wrote:
> > I agree that this patch do make sense, however, it seems to me this
> > patch should fix the problem that kobject is leaked, not uaf... And I
> > verified that the problem can still be reporduced with this patch.
>
> Can you share your reproducer?
> .

Of course, I add some delay in kernel to make sure the problem is
reproduced 100%:

diff --git a/block/holder.c b/block/holder.c
index 5283bc804cc1..be8f4b4245f3 100644
--- a/block/holder.c
+++ b/block/holder.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-only
 #include <linux/blkdev.h>
 #include <linux/slab.h>
+#include <linux/delay.h>

 struct bd_holder_disk {
        struct list_head        list;
@@ -33,6 +34,8 @@ static int __link_disk_holder(struct block_device 
*bdev, struct gendisk *disk)
 {
        int ret;

+       printk("%s: delay 5s\n", __func__);
+       msleep(5000);
        ret = add_symlink(disk->slave_dir, bdev_kobj(bdev));
        if (ret)
                return ret;

test cmd is very simple:

dmsetup create test1 --table "0 100000 linear /dev/sda 0" &
sleep 1
echo 1 > /sys/block/sda/device/delete