block: fix use-after-free in disk_part_iter_next

BugLink: https://bugs.launchpad.net/bugs/1913487
commit aebf5db917055b38f4945ed6d621d9f07a44ff30 upstream.

Make sure that bdgrab() is done on the 'block_device' instance before
referring to it for avoiding use-after-free.

Cc: <stable@vger.kernel.org>
Reported-by: syzbot+825f0f9657d4e528046e@syzkaller.appspotmail.com
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: William Breathitt Gray <william.gray@canonical.com>

diff --git a/block/genhd.c b/block/genhd.c
index 26b31fcae217fd3d936ccb32c6d7847ff5654805..604f0a2cbc9a072853c497a4c6d77a7600b9f47d 100644 (file)
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -222,14 +222,17 @@ struct hd_struct *disk_part_iter_next(struct disk_part_iter *piter)
                part = rcu_dereference(ptbl->part[piter->idx]);
                if (!part)
                        continue;
+               get_device(part_to_dev(part));
+               piter->part = part;
                if (!part_nr_sects_read(part) &&
                    !(piter->flags & DISK_PITER_INCL_EMPTY) &&
                    !(piter->flags & DISK_PITER_INCL_EMPTY_PART0 &&
-                     piter->idx == 0))
+                     piter->idx == 0)) {
+                       put_device(part_to_dev(part));
+                       piter->part = NULL;
                        continue;
+               }
 
-               get_device(part_to_dev(part));
-               piter->part = part;
                piter->idx += inc;
                break;
        }