Re: [PATCH] ubi: block: fix null-pointer-dereference in ubiblock_create()

From: Li Nan <linan666@huaweicloud.com>
To: Zhihao Cheng <chengzhihao1@huawei.com>,
	richard@nod.at, miquel.raynal@bootlin.com, vigneshr@ti.com,
	axboe@kernel.dk, chaitanya.kulkarni@wdc.com
Cc: linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org,
	yukuai3@huawei.com, yi.zhang@huawei.com, houtao1@huawei.com,
	yangerkun@huawei.com
Subject: Re: [PATCH] ubi: block: fix null-pointer-dereference in ubiblock_create()
Date: Mon, 6 May 2024 21:35:22 +0800	[thread overview]
Message-ID: <9bad9355-5b5a-de61-8c53-6e65ed3332b1@huaweicloud.com> (raw)
In-Reply-To: <98698009-e3a2-5c00-7619-6b6e3422cd1b@huawei.com>

在 2024/4/28 15:51, Zhihao Cheng 写道:
> 在 2024/4/28 15:19, linan666@huaweicloud.com 写道:
>> From: Li Nan <linan122@huawei.com>
>>
>> Similar to commit adbf4c4954e3 ("ubi: block: fix memleak in
>> ubiblock_create()"), 'dev->gd' is not assigned but dereferenced if
>> blk_mq_alloc_tag_set() fails, and leading to a null-pointer-dereference.
>>
>> Using 'gd' directly here is not a good idea, too. 'gd->part0.bd_device'
>> is not initialized at this point. The error log will be:
>>    block (null): block: dynamic minor allocation failed
>>
>> Fix it by using pr_err() and print ubi id.
>>
>> Fixes: 77567b25ab9f ("ubi: use blk_mq_alloc_disk and blk_cleanup_disk")
>> Signed-off-by: Li Nan <linan122@huawei.com>
>> ---
>>   drivers/mtd/ubi/block.c | 7 ++++---
>>   1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/mtd/ubi/block.c b/drivers/mtd/ubi/block.c
>> index f82e3423acb9..bf7308e8ec2f 100644
>> --- a/drivers/mtd/ubi/block.c
>> +++ b/drivers/mtd/ubi/block.c
>> @@ -390,7 +390,8 @@ int ubiblock_create(struct ubi_volume_info *vi)
>>       ret = blk_mq_alloc_tag_set(&dev->tag_set);
>>       if (ret) {
>> -        dev_err(disk_to_dev(dev->gd), "blk_mq_alloc_tag_set failed");
>> +        pr_err("ubiblock%d_%d: blk_mq_alloc_tag_set failed\n",
>> +            dev->ubi_num, dev->vol_id);
>>           goto out_free_dev;
>>       }
>> @@ -407,8 +408,8 @@ int ubiblock_create(struct ubi_volume_info *vi)
>>       gd->minors = 1;
>>       gd->first_minor = idr_alloc(&ubiblock_minor_idr, dev, 0, 0, 
>> GFP_KERNEL);
> 
> There is no need to modify this place. The device of 'gd' is initialized in 
> blk_mq_alloc_disk. Refer to nbd_dev_add.

The print of this dev_err() is:
   block (null): block: dynamic minor allocation failed
	~~~~~~
There is no information about which device failed. dev_err()
use 'kobject_name(&dev->kobj)' here, which is init in device_add_disk()
later. So use pr_err() here can print more detail.

I will split the patch into two in v2 to make it clearer.

>>       if (gd->first_minor < 0) {
>> -        dev_err(disk_to_dev(gd),
>> -            "block: dynamic minor allocation failed");
>> +        pr_err("ubiblock%d_%d: block: dynamic minor allocation failed\n",
>> +            dev->ubi_num, dev->vol_id);
>>           ret = -ENODEV;
>>           goto out_cleanup_disk;
>>       }
>>

-- 
Thanks,
Nan

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