From 62f535e1f061b4c2cc76061b6b59af9f9335ee34 Mon Sep 17 00:00:00 2001 From: Yu Kuai Date: Tue, 15 Nov 2022 22:10:52 +0800 Subject: [PATCH] block: fix use after free for bd_holder_dir Currently, the caller of bd_link_disk_holer() get 'bdev' by blkdev_get_by_dev(), which will look up 'bdev' by inode number 'dev'. Howerver, it's possible that del_gendisk() can be called currently, and 'bd_holder_dir' can be freed before bd_link_disk_holer() access it, thus use after free is triggered. t1: t2: bdev = blkdev_get_by_dev del_gendisk kobject_put(bd_holder_dir) kobject_free() bd_link_disk_holder Fix the problem by checking disk is still live and grabbing a reference to 'bd_holder_dir' first in bd_link_disk_holder(). Signed-off-by: Yu Kuai Reviewed-by: Christoph Hellwig Link: https://lore.kernel.org/r/20221115141054.1051801-9-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe --- block/holder.c | 21 +++++++++++++++------ 1 file changed, 15 insertions(+), 6 deletions(-) diff --git a/block/holder.c b/block/holder.c index dd9327b43ce0..c8e462053f49 100644 --- a/block/holder.c +++ b/block/holder.c @@ -65,12 +65,24 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk) if (WARN_ON_ONCE(!disk->slave_dir)) return -EINVAL; - mutex_lock(&disk->open_mutex); + /* + * del_gendisk drops the initial reference to bd_holder_dir, so we + * need to keep our own here to allow for cleanup past that point. + */ + mutex_lock(&bdev->bd_disk->open_mutex); + if (!disk_live(bdev->bd_disk)) { + mutex_unlock(&bdev->bd_disk->open_mutex); + return -ENODEV; + } + kobject_get(bdev->bd_holder_dir); + mutex_unlock(&bdev->bd_disk->open_mutex); + mutex_lock(&disk->open_mutex); WARN_ON_ONCE(!bdev->bd_holder); holder = bd_find_holder_disk(bdev, disk); if (holder) { + kobject_put(bdev->bd_holder_dir); holder->refcnt++; goto out_unlock; } @@ -92,11 +104,6 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk) goto out_del_symlink; list_add(&holder->list, &disk->slave_bdevs); - /* - * del_gendisk drops the initial reference to bd_holder_dir, so we need - * to keep our own here to allow for cleanup past that point. - */ - kobject_get(bdev->bd_holder_dir); mutex_unlock(&disk->open_mutex); return 0; @@ -106,6 +113,8 @@ out_free_holder: kfree(holder); out_unlock: mutex_unlock(&disk->open_mutex); + if (ret) + kobject_put(bdev->bd_holder_dir); return ret; } EXPORT_SYMBOL_GPL(bd_link_disk_holder);