From b7d6c30333239f77f8e51423064a623acc7fd127 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Fri, 8 May 2020 16:17:55 +0800 Subject: block: fix use-after-free on cached last_lookup partition delete_partition() clears the cached last_lookup partition. However the .last_lookup cache may be overwritten by one IO path after it is cleared from delete_partition(). Then another IO path may use the cached deleting partition after hd_struct_free() is called, then use-after-free is triggered on the cached partition. Fixes the issue by the following approach: 1) always get the partition's refcount via hd_struct_try_get() before setting .last_lookup 2) move clearing .last_lookup from delete_partition() to hd_struct_free() which is the release handle of the partition's percpu-refcount, so that no IO path can cache deleteing partition via .last_lookup. It is one candidate approach of Yufen's patch[1] which adds overhead in fast path by indirect lookup which may introduce one extra cacheline in IO path. Also this patch relies on percpu-refcount's protection, and it is easier to understand and verify. [1] https://lore.kernel.org/linux-block/20200109013551.GB9655@ming.t460p/T/#t Reported-by: Yufen Yu Signed-off-by: Ming Lei Reviewed-by: Christoph Hellwig Cc: Christoph Hellwig Cc: Hou Tao Signed-off-by: Jens Axboe --- block/partitions/core.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) (limited to 'block/partitions') diff --git a/block/partitions/core.c b/block/partitions/core.c index 873999e2e2f2..8d8c87207fc2 100644 --- a/block/partitions/core.c +++ b/block/partitions/core.c @@ -288,6 +288,12 @@ static void hd_struct_free_work(struct work_struct *work) static void hd_struct_free(struct percpu_ref *ref) { struct hd_struct *part = container_of(ref, struct hd_struct, ref); + struct gendisk *disk = part_to_disk(part); + struct disk_part_tbl *ptbl = + rcu_dereference_protected(disk->part_tbl, 1); + + rcu_assign_pointer(ptbl->last_lookup, NULL); + put_device(disk_to_dev(disk)); INIT_RCU_WORK(&part->rcu_work, hd_struct_free_work); queue_rcu_work(system_wq, &part->rcu_work); @@ -309,8 +315,12 @@ void delete_partition(struct gendisk *disk, struct hd_struct *part) struct disk_part_tbl *ptbl = rcu_dereference_protected(disk->part_tbl, 1); + /* + * ->part_tbl is referenced in this part's release handler, so + * we have to hold the disk device + */ + get_device(disk_to_dev(part_to_disk(part))); rcu_assign_pointer(ptbl->part[part->partno], NULL); - rcu_assign_pointer(ptbl->last_lookup, NULL); kobject_put(part->holder_dir); device_del(part_to_dev(part)); -- cgit v1.2.3