Re: [PATCH 1/4] block: fix use-after-free on cached last_lookup partition

Yufen Yu
2020-02-21T03:05:25Z

Hi Guys,

Did this patch have been forgotten? So, ping...

Thanks,
Yufen

On 2020/1/9 14:21, Ming Lei wrote:
> 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 __delete_partition() 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
> __delete_partition() which is release handle of the partition's
> percpu-refcount, so that no IO path can overwrite .last_lookup after it
> is cleared in __delete_partition().
>
> 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 <yuyufen@huawei.com>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Hou Tao <houtao1@huawei.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> block/blk-core.c | 12 ------------
> block/genhd.c | 6 +++++-
> block/partition-generic.c | 10 +++++++++-
> include/linux/genhd.h | 1 +
> 4 files changed, 15 insertions(+), 14 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 089e890ab208..79599f5fd5b7 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1365,18 +1365,6 @@ void blk_account_io_start(struct request *rq, bool new_io)
> part_stat_inc(part, merges[rw]);
> } else {
> part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
> - if (!hd_struct_try_get(part)) {
> - /*
> - * The partition is already being removed,
> - * the request will be accounted on the disk only
> - *
> - * We take a reference on disk->part0 although that
> - * partition will never be deleted, so we can treat
> - * it as any other partition.
> - */
> - part = &rq->rq_disk->part0;
> - hd_struct_get(part);
> - }
> part_inc_in_flight(rq->q, part, rw);
> rq->part = part;
> }
> diff --git a/block/genhd.c b/block/genhd.c
> index ff6268970ddc..6029c94510f0 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -286,17 +286,21 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
> ptbl = rcu_dereference(disk->part_tbl);
>
> part = rcu_dereference(ptbl->last_lookup);
> - if (part && sector_in_part(part, sector))
> + if (part && sector_in_part(part, sector) && hd_struct_try_get(part))
> return part;
>
> for (i = 1; i < ptbl->len; i++) {
> part = rcu_dereference(ptbl->part[i]);
>
> if (part && sector_in_part(part, sector)) {
> + if (!hd_struct_try_get(part))
> + goto exit;
> rcu_assign_pointer(ptbl->last_lookup, part);
> return part;
> }
> }
> + exit:
> + hd_struct_get(&disk->part0);
> return &disk->part0;
> }
> EXPORT_SYMBOL_GPL(disk_map_sector_rcu);
> diff --git a/block/partition-generic.c b/block/partition-generic.c
> index 1d20c9cf213f..1739f750dbf2 100644
> --- a/block/partition-generic.c
> +++ b/block/partition-generic.c
> @@ -262,6 +262,12 @@ static void delete_partition_work_fn(struct work_struct *work)
> void __delete_partition(struct percpu_ref *ref)
> {
> struct hd_struct *part = container_of(ref, struct hd_struct, ref);
> + struct disk_part_tbl *ptbl =
> + rcu_dereference_protected(part->disk->part_tbl, 1);
> +
> + rcu_assign_pointer(ptbl->last_lookup, NULL);
> + put_device(disk_to_dev(part->disk));
> +
> INIT_RCU_WORK(&part->rcu_work, delete_partition_work_fn);
> queue_rcu_work(system_wq, &part->rcu_work);
> }
> @@ -283,8 +289,9 @@ void delete_partition(struct gendisk *disk, int partno)
> if (!part)
> return;
>
> + get_device(disk_to_dev(disk));
> rcu_assign_pointer(ptbl->part[partno], NULL);
> - rcu_assign_pointer(ptbl->last_lookup, NULL);
> +
> kobject_put(part->holder_dir);
> device_del(part_to_dev(part));
>
> @@ -349,6 +356,7 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno,
> p->nr_sects = len;
> p->partno = partno;
> p->policy = get_disk_ro(disk);
> + p->disk = disk;
>
> if (info) {
> struct partition_meta_info *pinfo = alloc_part_info(disk);
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index 8bb63027e4d6..1b09cfe00aa3 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -130,6 +130,7 @@ struct hd_struct {
> struct disk_stats dkstats;
> #endif
> struct percpu_ref ref;
> + struct gendisk *disk;
> struct rcu_work rcu_work;
> };
>
>