From b7d6c30333239f77f8e51423064a623acc7fd127 Mon Sep 17 00:00:00 2001
From: Ming Lei <ming.lei@redhat.com>
Date: Fri, 8 May 2020 16:17:55 +0800
Subject: [PATCH] block: fix use-after-free on cached last_lookup partition
Git-commit: b7d6c30333239f77f8e51423064a623acc7fd127
Patch-mainline: v5.8-rc1
References: bsc#1181062
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
(Coly Li: rebased for v4.12 based SUSE kernel)
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>
Signed-off-by: Coly Li <colyli@suse.de>
---
block/blk-core.c | 12 ------------
block/genhd.c | 15 ++++++++++++---
block/partition-generic.c | 12 +++++++++++-
3 files changed, 23 insertions(+), 16 deletions(-)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2783,18 +2783,6 @@ void blk_account_io_start(struct request
part_stat_inc(cpu, 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_round_stats(rq->q, cpu, part);
part_inc_in_flight(rq->q, part, rw);
rq->part = part;
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -257,11 +257,12 @@ static inline int sector_in_part(struct
* 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)
{
@@ -272,17 +273,25 @@ struct hd_struct *disk_map_sector_rcu(st
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;
}
EXPORT_SYMBOL_GPL(disk_map_sector_rcu);
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -246,6 +246,12 @@ struct device_type part_type = {
static void delete_partition_rcu_cb(struct rcu_head *head)
{
struct hd_struct *part = container_of(head, struct hd_struct, rcu_head);
+ 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));
part->start_sect = 0;
part->nr_sects = 0;
@@ -276,8 +282,12 @@ void delete_partition(struct gendisk *di
if (!part)
return;
+ /*
+ * ->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[partno], NULL);
- rcu_assign_pointer(ptbl->last_lookup, NULL);
kobject_put(part->holder_dir);
device_del(part_to_dev(part));