linux-kernel - Re: [PATCH] usb: storage: sddr55: Fix a possible null-pointer dereference in sddr55

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Date:   Mon, 29 Jul 2019 19:44:08 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     Oliver Neukum <oneukum@...e.com>, gregkh@...uxfoundation.org,
        stern@...land.harvard.edu
Cc:     usb-storage@...ts.one-eyed-alien.net, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH] usb: storage: sddr55: Fix a possible null-pointer
 dereference in sddr55_transport()



On 2019/7/29 19:15, Oliver Neukum wrote:
> Am Montag, den 29.07.2019, 18:05 +0800 schrieb Jia-Ju Bai:
>
> Hi,
>
>> In sddr55_transport(), there is an if statement on line 836 to check
>> whether info->lba_to_pba is NULL:
>>      if (info->lba_to_pba == NULL || ...)
>>
>> When info->lba_to_pba is NULL, it is used on line 948:
>>      pba = info->lba_to_pba[lba];
>>
>> Thus, a possible null-pointer dereference may occur.
> Yes, in practice READ_CAPACITY will always be called and set
> up the correct translation table, but you can probably exploit
> this.
>
>> To fix this bug, info->lba_to_pba is checked before being used.
>>
>> This bug is found by a static analysis tool STCheck written by us.
>>
>> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
>> ---
>>   drivers/usb/storage/sddr55.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/usb/storage/sddr55.c b/drivers/usb/storage/sddr55.c
>> index b8527c55335b..50afc39aa21d 100644
>> --- a/drivers/usb/storage/sddr55.c
>> +++ b/drivers/usb/storage/sddr55.c
>> @@ -945,7 +945,8 @@ static int sddr55_transport(struct scsi_cmnd *srb, struct us_data *us)
>>   			return USB_STOR_TRANSPORT_FAILED;
>>   		}
>>   
>> -		pba = info->lba_to_pba[lba];
>> +		if (info->lba_to_pba)
>> +			pba = info->lba_to_pba[lba];
> If you use that fix, pba will be uninitialized when used. It should be
> something like:
>
> pba = info->lba_to_pba ? info->lba_to_pba[lba] : 0;

Thanks for the advice.
I will send a v2 patch.


Best wishes,
Jia-Ju Bai