nbd: fix uaf in nbd_open

[ Upstream commit 327462725b0f759f093788dfbcb2f1fd132f956b ]

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 nbd has
been free in nbd_dev_remove().

Fix this by implementing ->free_disk and free private data in it.

Fixes: 4af5f2e03013 ("nbd: use blk_mq_alloc_disk and blk_cleanup_disk")
Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20231107103435.2074904-1-lilingfeng@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 800f131..855fdf5 100644 (file)
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -250,7 +250,6 @@ static void nbd_dev_remove(struct nbd_device *nbd)
        struct gendisk *disk = nbd->disk;
 
        del_gendisk(disk);
-       put_disk(disk);
        blk_mq_free_tag_set(&nbd->tag_set);
 
        /*
@@ -261,7 +260,7 @@ static void nbd_dev_remove(struct nbd_device *nbd)
        idr_remove(&nbd_index_idr, nbd->index);
        mutex_unlock(&nbd_index_mutex);
        destroy_workqueue(nbd->recv_workq);
-       kfree(nbd);
+       put_disk(disk);
 }
 
 static void nbd_dev_remove_work(struct work_struct *work)
@@ -1608,6 +1607,13 @@ static void nbd_release(struct gendisk *disk)
        nbd_put(nbd);
 }
 
+static void nbd_free_disk(struct gendisk *disk)
+{
+       struct nbd_device *nbd = disk->private_data;
+
+       kfree(nbd);
+}
+
 static const struct block_device_operations nbd_fops =
 {
        .owner =        THIS_MODULE,
@@ -1615,6 +1621,7 @@ static const struct block_device_operations nbd_fops =
        .release =      nbd_release,
        .ioctl =        nbd_ioctl,
        .compat_ioctl = nbd_ioctl,
+       .free_disk =    nbd_free_disk,
 };
 
 #if IS_ENABLED(CONFIG_DEBUG_FS)