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Subject: Re: [PATCH] UBI: fix use after free in ubi_remove_volume()
From:   Hou Tao <houtao1@huawei.com>
To:     Wen Yang <wenyang@linux.alibaba.com>,
        Richard Weinberger <richard@nod.at>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Vignesh Raghavendra <vigneshr@ti.com>
CC:     <linux-mtd@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
        <xlpang@linux.alibaba.com>
References: <20191130093317.31352-1-wenyang@linux.alibaba.com>
 <65b49705-e28c-e077-c0de-c5167e34d1c5@huawei.com>
Message-ID: <58208ceb-4d72-c4a1-8a2b-9e38854e3672@huawei.com>
Date:   Thu, 5 Dec 2019 09:33:18 +0800
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Hi,

On 2019/12/3 21:13, Hou Tao wrote:
> Reviewed-by: Hou Tao <houtao1@huawei.com>
> 
Sorry for my early conclusion.

The reference of ubi_volume had already been increased in ubi_open_volume()
in ubi_cdev_ioctl(), so this reference dropped in ubi_remove_volume() will not
be the last one, and there will no use-after-free problem.

Regards,
Tao

> On 2019/11/30 17:33, Wen Yang wrote:
>> We can't use "vol" after it has been freed.
>>
>> Fixes: 493cfaeaa0c9 ("mtd: utilize new cdev_device_add helper function")
>> Signed-off-by: Wen Yang <wenyang@linux.alibaba.com>
>> Cc: Richard Weinberger <richard@nod.at>
>> Cc: Miquel Raynal <miquel.raynal@bootlin.com>
>> Cc: Vignesh Raghavendra <vigneshr@ti.com>
>> Cc: linux-mtd@lists.infradead.org
>> Cc: linux-kernel@vger.kernel.org
>> ---
>>  drivers/mtd/ubi/vmt.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/mtd/ubi/vmt.c b/drivers/mtd/ubi/vmt.c
>> index 139ee13..8ff1478 100644
>> --- a/drivers/mtd/ubi/vmt.c
>> +++ b/drivers/mtd/ubi/vmt.c
>> @@ -375,7 +375,6 @@ int ubi_remove_volume(struct ubi_volume_desc *desc, int no_vtbl)
>>  	}
>>  
>>  	cdev_device_del(&vol->cdev, &vol->dev);
>> -	put_device(&vol->dev);
>>  
>>  	spin_lock(&ubi->volumes_lock);
>>  	ubi->rsvd_pebs -= reserved_pebs;
>> @@ -388,6 +387,8 @@ int ubi_remove_volume(struct ubi_volume_desc *desc, int no_vtbl)
>>  	if (!no_vtbl)
>>  		self_check_volumes(ubi);
>>  
>> +	put_device(&vol->dev);
>> +
>>  	return 0;
>>  
>>  out_err:
>>
> 
> 
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