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@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 | 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;
};
