Hello Yufen,
On Fri, Jan 03, 2020 at 08:03:54PM +0800, Yufen Yu wrote:
> Hi, Ming
>
> On 2020/1/3 16:17, Ming Lei wrote:
> >
> > We may avoid that by clearing partition pointer after killing the
> > partition, how about the following change?
> >
> > 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..e3dec90b1f43 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..9ef6c13d5650 100644
> > --- a/block/partition-generic.c
> > +++ b/block/partition-generic.c
> > @@ -283,8 +283,8 @@ void delete_partition(struct gendisk *disk, int partno)
> > if (!part)
> > return;
> > - rcu_assign_pointer(ptbl->part[partno], NULL);
> > - rcu_assign_pointer(ptbl->last_lookup, NULL);
> > + get_device(disk_to_dev(disk));
> > +
> > kobject_put(part->holder_dir);
> > device_del(part_to_dev(part));
> > @@ -296,6 +296,15 @@ void delete_partition(struct gendisk *disk, int partno)
> > */
> > blk_invalidate_devt(part_devt(part));
> > hd_struct_kill(part);
> > +
> > + /*
> > + * clear partition pointers after this partition is killed, then
> > + * IO path can't re-assign ->last_lookup any more
> > + */
> > + rcu_assign_pointer(ptbl->part[partno], NULL);
> > + rcu_assign_pointer(ptbl->last_lookup, NULL);
> > +
> > + put_device(disk_to_dev(disk));
> > }
>
> This change may cannot solve follow case:
>
> disk_map_sector_rcu delete_partition disk_map_sector_rcu
> hd_struct_try_get(part)
> hd_struct_kill
> last_lookup = NULL;
> last_lookup = part
>
>
> call_rcu
> read last_lookup
>
> free()
> //use-after-free
> sector_in_part(part, sector)
>
> There is an interval between getting part and setting last_lookup
> in disk_map_sector_rcu(). If we kill the part and clear last_lookup
> at that interval, last_lookup will be re-assign again, which can cause
> use-after-free for readers after call_rcu.
OK, we still can move clearing .last_lookup into __delete_partition(),
at that time all IO path can observe the partition percpu-refcount killed.
Also the rcu work fn is run after one RCU grace period, at that time,
the NULL .last_lookup becomes visible in all IO path too.
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..e3dec90b1f43 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..66660ec5e8ee 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -129,6 +129,7 @@ struct hd_struct {
#else
struct disk_stats dkstats;
#endif
+ struct gendisk *disk;
struct percpu_ref ref;
struct rcu_work rcu_work;
};
Thanks,
Ming
