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 <yuyufen@xxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> Cc: Hou Tao <houtao1@xxxxxxxxxx> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> --- block/blk-core.c | 12 ------------ block/genhd.c | 15 ++++++++++++--- block/partitions/core.c | 12 +++++++++++- 3 files changed, 23 insertions(+), 16 deletions(-) diff --git a/block/blk-core.c b/block/blk-core.c index ec50d7e6be21..826a8980997d 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -1363,18 +1363,6 @@ 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 c05d509877fa..ec57d5d7a64d 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -344,11 +344,12 @@ static inline int sector_in_part(struct hd_struct *part, sector_t sector) * primarily used for stats accounting. * * CONTEXT: - * RCU read locked. The returned partition pointer is valid only - * while preemption is disabled. + * RCU read locked. The returned partition pointer is always valid + * because its refcount is grabbed. * * RETURNS: * Found partition on success, part0 is returned if no partition matches + * or the matched partition is being deleted. */ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector) { @@ -359,17 +360,25 @@ 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)) { + /* + * only live partition can be cached for lookup, + * so use-after-free on cached & deleting partition + * can be avoided + */ + if (!hd_struct_try_get(part)) + break; rcu_assign_pointer(ptbl->last_lookup, part); return part; } } + hd_struct_get(&disk->part0); return &disk->part0; } diff --git a/block/partitions/core.c b/block/partitions/core.c index c085bf85509b..f4000dac23ef 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)); -- 2.25.2
