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From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: axboe@kernel.dk, Christoph Hellwig <hch@lst.de>
Cc: linux-block@vger.kernel.org
Subject: [PATCH] block: genhd: fix double kfree() in __alloc_disk_node()
Date: Sun, 19 Sep 2021 23:44:29 +0900	[thread overview]
Message-ID: <3999c511-cd27-1554-d3a6-4288c3eca298@i-love.sakura.ne.jp> (raw)
In-Reply-To: <41766564-08cb-e7f2-4cb2-9ad102f21324@I-love.SAKURA.ne.jp>

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 explicitly resetting bdev->bd_disk to NULL before 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>
---
This patch is not tested due to lack of reproducer. Is this fix correct?

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

diff --git a/block/bdev.c b/block/bdev.c
index cf2780cb44a7..f6b8bac83bd8 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -495,6 +495,7 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
 	bdev->bd_inode = inode;
 	bdev->bd_stats = alloc_percpu(struct disk_stats);
 	if (!bdev->bd_stats) {
+		bdev->bd_disk = NULL;
 		iput(inode);
 		return NULL;
 	}
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:[~2021-09-19 14:44 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   ` Tetsuo Handa [this message]
2021-09-20  6:40     ` [PATCH] block: genhd: fix double kfree() in __alloc_disk_node() Christoph Hellwig
2021-09-20  8:02       ` Tetsuo Handa
2021-09-20  8:05         ` Christoph Hellwig
2021-09-20  8:31           ` [PATCH v2] " Tetsuo Handa
2021-09-20  8:40             ` Christoph Hellwig
2021-10-09  4:53 ` [syzbot] KASAN: use-after-free Read in bdev_free_inode syzbot

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