linux-kernel - Re: [PATCH] scsi: target: pscsi: Fix possible null-pointer dereference in pscsi_complete

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Message-ID: <7c6622d0-2f28-27a7-250e-9a8fd79691a8@gmail.com>
Date:   Mon, 9 Aug 2021 19:50:37 +0800
From:   Tuo Li <islituo@...il.com>
To:     Bodo Stroesser <bostroesser@...il.com>
Cc:     linux-scsi@...r.kernel.org, target-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org, baijiaju1990@...il.com,
        TOTE Robot <oslab@...nghua.edu.cn>, martin.petersen@...cle.com
Subject: Re: [PATCH] scsi: target: pscsi: Fix possible null-pointer
 dereference in pscsi_complete_cmd()

Thanks for your feedback. We will prepare a V2 patch and put the 
transport_kunmap_data_sg()
into the else-branch of the if (!buf).

Best wishes,
Tuo Li

On 2021/8/9 18:36, Bodo Stroesser wrote:
> On 07.08.21 15:46, Tuo Li wrote:
>> The return value of transport_kmap_data_sg() is assigned to the variable
>> buf:
>>    buf = transport_kmap_data_sg(cmd);
>>
>> And then it is checked:
>>    if (!buf) {
>>
>> This indicates that buf can be NULL. However, it is dereferenced in the
>> following statements:
>>    if (!(buf[3] & 0x80))
>>      buf[3] |= 0x80;
>>    if (!(buf[2] & 0x80))
>>     buf[2] |= 0x80;
>>
>> To fix these possible null-pointer dereferences, dereference buf only 
>> when
>> it is not NULL.
>>
>> Reported-by: TOTE Robot <oslab@...nghua.edu.cn>
>> Signed-off-by: Tuo Li <islituo@...il.com>
>> ---
>>   drivers/target/target_core_pscsi.c | 14 +++++++-------
>>   1 file changed, 7 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/target/target_core_pscsi.c 
>> b/drivers/target/target_core_pscsi.c
>> index 2629d2ef3970..560815729182 100644
>> --- a/drivers/target/target_core_pscsi.c
>> +++ b/drivers/target/target_core_pscsi.c
>> @@ -620,14 +620,14 @@ static void pscsi_complete_cmd(struct se_cmd 
>> *cmd, u8 scsi_status,
>>               buf = transport_kmap_data_sg(cmd);
>>               if (!buf) {
>>                   ; /* XXX: TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE */
>> -            }
>> -
>> -            if (cdb[0] == MODE_SENSE_10) {
>> -                if (!(buf[3] & 0x80))
>> -                    buf[3] |= 0x80;
>>               } else {
>> -                if (!(buf[2] & 0x80))
>> -                    buf[2] |= 0x80;
>> +                if (cdb[0] == MODE_SENSE_10) {
>> +                    if (!(buf[3] & 0x80))
>> +                        buf[3] |= 0x80;
>> +                } else {
>> +                    if (!(buf[2] & 0x80))
>> +                        buf[2] |= 0x80;
>> +                }
>>               }
>>                 transport_kunmap_data_sg(cmd);
>>
>
> I'm wondering whether we should better put the
> transport_kunmap_data_sg into the else-branch of the if (!buf)?
> AFAICS, calling it after transport_kmap_data_sg failed does not
> cause problems, but I feel it would be cleaner.
>
> Otherwise it looks good to me.