[Linux-kernel-mentees] [PATCH] block: Fix use-after-free in bdev_del_partition()

[Peilin Ye]

In bdev_del_partition(), `part` is being looked up outside the critical
section. This is causing bdev_del_partition() to delete the same partition
more than once. Fix it by reverting commit cddae808aeb7.

Fixes: cddae808aeb7 ("block: pass a hd_struct to delete_partition")
Reported-and-tested-by: syzbot+6448f3c229bc52b82...@syzkaller.appspotmail.com
Cc: sta...@vger.kernel.org
Cc: Hillf Danton <hdan...@sina.com>
Link: 
https://syzkaller.appspot.com/bug?id=09fc5ec437ea150f28e8a19f5011c08ee73381af
Signed-off-by: Peilin Ye <yepeilin...@gmail.com>
---
 block/blk.h             |  2 +-
 block/genhd.c           |  2 +-
 block/partitions/core.c | 22 ++++++++++++++--------
 3 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/block/blk.h b/block/blk.h
index 49e2928a1632..f5a46d0020fb 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -350,7 +350,7 @@ char *disk_name(struct gendisk *hd, int partno, char *buf);
 #define ADDPART_FLAG_NONE      0
 #define ADDPART_FLAG_RAID      1
 #define ADDPART_FLAG_WHOLEDISK 2
-void delete_partition(struct gendisk *disk, struct hd_struct *part);
+void delete_partition(struct gendisk *disk, int partno);
 int bdev_add_partition(struct block_device *bdev, int partno,
                sector_t start, sector_t length);
 int bdev_del_partition(struct block_device *bdev, int partno);
diff --git a/block/genhd.c b/block/genhd.c
index 99c64641c314..40abc70b92ab 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -913,7 +913,7 @@ void del_gendisk(struct gendisk *disk)
                             DISK_PITER_INCL_EMPTY | DISK_PITER_REVERSE);
        while ((part = disk_part_iter_next(&piter))) {
                invalidate_partition(disk, part->partno);
-               delete_partition(disk, part);
+               delete_partition(disk, part->partno);
        }
        disk_part_iter_exit(&piter);
 
diff --git a/block/partitions/core.c b/block/partitions/core.c
index e62a98a8eeb7..1fe1fe593423 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -310,17 +310,25 @@ int hd_ref_init(struct hd_struct *part)
  * Must be called either with bd_mutex held, before a disk can be opened or
  * after all disk users are gone.
  */
-void delete_partition(struct gendisk *disk, struct hd_struct *part)
+void delete_partition(struct gendisk *disk, int partno)
 {
        struct disk_part_tbl *ptbl =
                rcu_dereference_protected(disk->part_tbl, 1);
+       struct hd_struct *part;
+
+       if (partno >= ptbl->len)
+               return;
+
+       part = rcu_dereference_protected(ptbl->part[partno], 1);
+       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[part->partno], NULL);
+       rcu_assign_pointer(ptbl->part[partno], NULL);
        kobject_put(part->holder_dir);
        device_del(part_to_dev(part));
 
@@ -531,10 +539,10 @@ int bdev_del_partition(struct block_device *bdev, int 
partno)
        if (!part)
                return -ENXIO;
 
-       ret = -ENOMEM;
        bdevp = bdget(part_devt(part));
+       disk_put_part(part);
        if (!bdevp)
-               goto out_put_part;
+               return -ENOMEM;
 
        mutex_lock(&bdevp->bd_mutex);
 
@@ -546,15 +554,13 @@ int bdev_del_partition(struct block_device *bdev, int 
partno)
        invalidate_bdev(bdevp);
 
        mutex_lock_nested(&bdev->bd_mutex, 1);
-       delete_partition(bdev->bd_disk, part);
+       delete_partition(bdev->bd_disk, partno);
        mutex_unlock(&bdev->bd_mutex);
 
        ret = 0;
 out_unlock:
        mutex_unlock(&bdevp->bd_mutex);
        bdput(bdevp);
-out_put_part:
-       disk_put_part(part);
        return ret;
 }
 
@@ -627,7 +633,7 @@ int blk_drop_partitions(struct block_device *bdev)
 
        disk_part_iter_init(&piter, bdev->bd_disk, DISK_PITER_INCL_EMPTY);
        while ((part = disk_part_iter_next(&piter)))
-               delete_partition(bdev->bd_disk, part);
+               delete_partition(bdev->bd_disk, part->partno);
        disk_part_iter_exit(&piter);
 
        return 0;
-- 
2.25.1