linux-kernel - Re: [PATCH] scsi: ibmvscsis: Fix a stringop-overflow warning

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Date:   Tue, 11 Sep 2018 09:34:57 -0500
From:   "Bryant G. Ly" <bryantly@...ux.ibm.com>
To:     Kees Cook <keescook@...omium.org>,
        Laura Abbott <labbott@...hat.com>
Cc:     "Bryant G. Ly" <bryantly@...ux.vnet.ibm.com>,
        Michael Cyr <mikecyr@...ux.vnet.ibm.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org,
        target-devel <target-devel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Prarit Bhargava <prarit@...hat.com>
Subject: Re: [PATCH] scsi: ibmvscsis: Fix a stringop-overflow warning

On 9/10/18 6:30 PM, Kees Cook wrote:

> On Mon, Sep 10, 2018 at 3:37 PM, Laura Abbott <labbott@...hat.com> wrote:
>> There's currently a warning about string overflow with strncat:
>>
>> drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c: In function 'ibmvscsis_probe':
>> drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c:3479:2: error: 'strncat' specified
>> bound 64 equals destination size [-Werror=stringop-overflow=]
>>   strncat(vscsi->eye, vdev->name, MAX_EYE);
>>   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> Switch to using strlcat which correctly accounts for lengths that
>> are equal to the destination buffer.
>>
>> Signed-off-by: Laura Abbott <labbott@...hat.com>
>> ---
>>  drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c b/drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c
>> index fac377320158..53d344d8dc43 100644
>> --- a/drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c
>> +++ b/drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c
>> @@ -3475,7 +3475,7 @@ static int ibmvscsis_probe(struct vio_dev *vdev,
>>                 vscsi->dds.window[REMOTE].liobn);
>>
>>         strcpy(vscsi->eye, "VSCSI ");
>> -       strncat(vscsi->eye, vdev->name, MAX_EYE);
>> +       strlcat(vscsi->eye, vdev->name, MAX_EYE);
> Can this just get switched to snprintf() instead?
>
> snprintf(vscsi->eye, sizeof(vscsi->eye), "VSCSI%s", vdev->name);

Either works for me. 

>
>>         vscsi->dds.unit_id = vdev->unit_address;
>>         strncpy(vscsi->dds.partition_name, partition_name,
> And does this strncpy need a NUL-termination and/or trailing padding?
>
Yes, good catch, it does need NUL-termination. 

-Bryant