2023-11-03 02:18:45

by Li Lingfeng

Subject: [PATCH] nbd: fix uaf in nbd_open

From: Li Lingfeng <[email protected]>

Commit 4af5f2e03013 ("nbd: use blk_mq_alloc_disk and
blk_cleanup_disk") cleans up disk by blk_cleanup_disk() and it won't set
disk->private_data as NULL as before. UAF may be triggered in nbd_open()
if someone tries to open nbd device right after nbd_put() since refcount
of nbd device is zero and private_data is not NULL.

Fixes: 4af5f2e03013 ("nbd: use blk_mq_alloc_disk and blk_cleanup_disk")
Signed-off-by: Li Lingfeng <[email protected]>
---
drivers/block/nbd.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 800f131222fc..aab93b836e84 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -250,6 +250,7 @@ static void nbd_dev_remove(struct nbd_device *nbd)
struct gendisk *disk = nbd->disk;

del_gendisk(disk);
+ disk->private_data = NULL;
put_disk(disk);
blk_mq_free_tag_set(&nbd->tag_set);

--
2.31.1

2023-11-03 03:30:48

by Yu Kuai

Subject: Re: [PATCH] nbd: fix uaf in nbd_open

Hi,

?? 2023/11/03 18:13, Li Lingfeng д??:
> From: Li Lingfeng <[email protected]>
>
> Commit 4af5f2e03013 ("nbd: use blk_mq_alloc_disk and
> blk_cleanup_disk") cleans up disk by blk_cleanup_disk() and it won't set
> disk->private_data as NULL as before. UAF may be triggered in nbd_open()
> if someone tries to open nbd device right after nbd_put() since refcount
> of nbd device is zero and private_data is not NULL.
>
Do you mean that nbd_open concurrent with nbd_dev_remove?

nbd_open nbd_dev_remove
del_gendisk
kfree(nbd)
mutex_lock
nbd = disk->private_data
-> UAF
refcount_inc_not_zero

Looks like it's possible, but you should use READ/WRITE_ONCE() here,
because disk->pravate_data can be accessed concurrently.

Thanks,
Kuai

> Fixes: 4af5f2e03013 ("nbd: use blk_mq_alloc_disk and blk_cleanup_disk")
> Signed-off-by: Li Lingfeng <[email protected]>
> ---
> drivers/block/nbd.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 800f131222fc..aab93b836e84 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -250,6 +250,7 @@ static void nbd_dev_remove(struct nbd_device *nbd)
> struct gendisk *disk = nbd->disk;
>
> del_gendisk(disk);
> + disk->private_data = NULL;
> put_disk(disk);
> blk_mq_free_tag_set(&nbd->tag_set);
>
>

2023-11-03 08:13:10

by Christoph Hellwig

Subject: Re: [PATCH] nbd: fix uaf in nbd_open

On Fri, Nov 03, 2023 at 06:13:34PM +0800, Li Lingfeng wrote:
> From: Li Lingfeng <[email protected]>
>
> Commit 4af5f2e03013 ("nbd: use blk_mq_alloc_disk and
> blk_cleanup_disk") cleans up disk by blk_cleanup_disk() and it won't set
> disk->private_data as NULL as before. UAF may be triggered in nbd_open()
> if someone tries to open nbd device right after nbd_put() since refcount
> of nbd device is zero and private_data is not NULL.

I don't think this is the right fix. nbd needs to move to ->free_disk
to free it's private data.

2023-11-06 12:47:03

by Li Lingfeng

Subject: Re: [PATCH] nbd: fix uaf in nbd_open

在 2023/11/3 16:12, Christoph Hellwig 写道:
> On Fri, Nov 03, 2023 at 06:13:34PM +0800, Li Lingfeng wrote:
>> From: Li Lingfeng <[email protected]>
>>
>> Commit 4af5f2e03013 ("nbd: use blk_mq_alloc_disk and
>> blk_cleanup_disk") cleans up disk by blk_cleanup_disk() and it won't set
>> disk->private_data as NULL as before. UAF may be triggered in nbd_open()
>> if someone tries to open nbd device right after nbd_put() since refcount
>> of nbd device is zero and private_data is not NULL.
> I don't think this is the right fix. nbd needs to move to ->free_disk
> to free it's private data.
Thanks for your advice, I will send v2 soon.