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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 <yuyufen@huawei.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hou Tao <houtao1@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2020-05-08 16:17:55 +08:00 committed by Jens Axboe
parent aa880ad690
commit b7d6c30333
3 changed files with 23 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
block/blk-core.c
View File

@ -1362,18 +1362,6 @@ 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;
}

15
block/genhd.c
View File

@ -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;
}

12
block/partitions/core.c
View File

@ -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));