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From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Christoph Hellwig <hch@lst.de>
Cc: axboe@kernel.dk, linux-block@vger.kernel.org
Subject: [PATCH v2] block: genhd: fix double kfree() in __alloc_disk_node()
Date: Mon, 20 Sep 2021 17:31:38 +0900	[thread overview]
Message-ID: <692fdc1a-6396-dcf4-c700-2d822f161053@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20210920080547.GA30362@lst.de>

syzbot is reporting use-after-free read at bdev_free_inode() [1], for
kfree() from __alloc_disk_node() is called before bdev_free_inode()
(which is called after RCU grace period) reads bdev->bd_disk and calls
kfree(bdev->bd_disk).

Fix use-after-free read followed by double kfree() problem
by making sure that bdev->bd_disk is NULL when calling iput().

Link: https://syzkaller.appspot.com/bug?extid=8281086e8a6fbfbd952a [1]
Reported-by: syzbot <syzbot+8281086e8a6fbfbd952a@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
Changes in v2:
  Defer bdev->bd_disk assignment instead of resetting to NULL in bdev_alloc().

 block/bdev.c  | 2 +-
 block/genhd.c | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/bdev.c b/block/bdev.c
index cf2780cb44a7..485a258b0ab3 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -490,7 +490,6 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
 	bdev = I_BDEV(inode);
 	mutex_init(&bdev->bd_fsfreeze_mutex);
 	spin_lock_init(&bdev->bd_size_lock);
-	bdev->bd_disk = disk;
 	bdev->bd_partno = partno;
 	bdev->bd_inode = inode;
 	bdev->bd_stats = alloc_percpu(struct disk_stats);
@@ -498,6 +497,7 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
 		iput(inode);
 		return NULL;
 	}
+	bdev->bd_disk = disk;
 	return bdev;
 }
 
diff --git a/block/genhd.c b/block/genhd.c
index 7b6e5e1cf956..496e8458c357 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1268,6 +1268,7 @@ struct gendisk *__alloc_disk_node(struct request_queue *q, int node_id,
 
 out_destroy_part_tbl:
 	xa_destroy(&disk->part_tbl);
+	disk->part0->bd_disk = NULL;
 	iput(disk->part0->bd_inode);
 out_free_bdi:
 	bdi_put(disk->bdi);
-- 
2.18.4


  reply	other threads:[~2021-09-20  8:31 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-19 13:35 [syzbot] KASAN: use-after-free Read in bdev_free_inode syzbot
2021-09-19 13:37 ` Tetsuo Handa
2021-09-19 14:44   ` [PATCH] block: genhd: fix double kfree() in __alloc_disk_node() Tetsuo Handa
2021-09-20  6:40     ` Christoph Hellwig
2021-09-20  8:02       ` Tetsuo Handa
2021-09-20  8:05         ` Christoph Hellwig
2021-09-20  8:31           ` Tetsuo Handa [this message]
2021-09-20  8:40             ` [PATCH v2] " Christoph Hellwig
2021-10-09  4:53 ` [syzbot] KASAN: use-after-free Read in bdev_free_inode syzbot

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