linux-hardening - Re: [PATCH] scsi: ibmvscsi_tgt: replace deprecated strncpy with strscpy

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Message-ID: <40483b3e-d820-4a9c-823d-76d6f24edfd6@gmail.com>
Date: Thu, 18 Jan 2024 12:19:09 -0800
From: Tyrel Datwyler <turtle.in.the.kernel@...il.com>
To: Kees Cook <keescook@...omium.org>, Justin Stitt <justinstitt@...gle.com>
Cc: Michael Cyr <mikecyr@...ux.ibm.com>,
 "James E.J. Bottomley" <jejb@...ux.ibm.com>,
 "Martin K. Petersen" <martin.petersen@...cle.com>,
 linux-scsi@...r.kernel.org, target-devel@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] scsi: ibmvscsi_tgt: replace deprecated strncpy with
 strscpy

On 11/30/23 13:25, Kees Cook wrote:
> On Mon, Oct 30, 2023 at 09:43:20PM +0000, Justin Stitt wrote:
>> strncpy() is deprecated for use on NUL-terminated destination strings
>> [1] and as such we should prefer more robust and less ambiguous string
>> interfaces.
>>
>> We don't need the NUL-padding behavior that strncpy() provides as vscsi
>> is NUL-allocated in ibmvscsis_probe() which proceeds to call
>> ibmvscsis_adapter_info():
>> |       vscsi = kzalloc(sizeof(*vscsi), GFP_KERNEL);
>>
>> ibmvscsis_probe() -> ibmvscsis_handle_crq() -> ibmvscsis_parse_command()
>> -> ibmvscsis_mad() -> ibmvscsis_process_mad() -> ibmvscsis_adapter_info()
>>
>> Following the same idea, `partition_name` is defiend as:
>> |       static char partition_name[PARTITION_NAMELEN] = "UNKNOWN";
>>
>> ... which is NUL-padded already, meaning strscpy() is the best option.
>>
>> Considering the above, a suitable replacement is `strscpy` [2] due to
>> the fact that it guarantees NUL-termination on the destination buffer
>> without unnecessarily NUL-padding.
> 
> My only worry here is that I don't see if %NUL termination is _required_
> for these variables. (i.e. do we run the risk of truncating these by 1
> byte if they're right at the limit?) Are they __nonstring?
> 
> I *think* they're %NUL terminated since they follow the same sizing as
> the global "partition_name", but I'm not sure.
> 
> Can any of the SCSI authors comment on this?

Sorry, for a delayed response. I've just taken over the maintainer role as it
had been left unaccounted for sometime.

These are meant to be handled as C strings and nul termination is expected.

-Tyrel

> 
>>
>> However, for cap->name let's use strscpy_pad as cap is allocated via
>> dma_alloc_coherent():
>> |       cap = dma_alloc_coherent(&vscsi->dma_dev->dev, olen, &token,
>> |                                GFP_ATOMIC);
> 
> This is also true for the "info" allocation (it comes out of DMA).
> 
>>
>> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
>> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
>> Link: https://github.com/KSPP/linux/issues/90
>> Cc: linux-hardening@...r.kernel.org
>> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
>> ---
>> Note: build-tested only.
>>
>> Found with: $ rg "strncpy\("
>> ---
>>  drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c | 14 +++++++-------
>>  1 file changed, 7 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c b/drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c
>> index 385f812b8793..cd223ef696e5 100644
>> --- a/drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c
>> +++ b/drivers/scsi/ibmvscsi_tgt/ibmvscsi_tgt.c
>> @@ -1551,17 +1551,17 @@ static long ibmvscsis_adapter_info(struct scsi_info *vscsi,
>>  	if (vscsi->client_data.partition_number == 0)
>>  		vscsi->client_data.partition_number =
>>  			be32_to_cpu(info->partition_number);
>> -	strncpy(vscsi->client_data.srp_version, info->srp_version,
>> +	strscpy(vscsi->client_data.srp_version, info->srp_version,
>>  		sizeof(vscsi->client_data.srp_version));
>> -	strncpy(vscsi->client_data.partition_name, info->partition_name,
>> +	strscpy(vscsi->client_data.partition_name, info->partition_name,
>>  		sizeof(vscsi->client_data.partition_name));
>>  	vscsi->client_data.mad_version = be32_to_cpu(info->mad_version);
>>  	vscsi->client_data.os_type = be32_to_cpu(info->os_type);
>>  
>>  	/* Copy our info */
>> -	strncpy(info->srp_version, SRP_VERSION,
>> +	strscpy(info->srp_version, SRP_VERSION,
>>  		sizeof(info->srp_version));
>> -	strncpy(info->partition_name, vscsi->dds.partition_name,
>> +	strscpy(info->partition_name, vscsi->dds.partition_name,
>>  		sizeof(info->partition_name));
> 
> Since "info" is from DMA, let's use the _pad variant here just to be
> safe.
> 
>>  	info->partition_number = cpu_to_be32(vscsi->dds.partition_num);
>>  	info->mad_version = cpu_to_be32(MAD_VERSION_1);
>> @@ -1645,8 +1645,8 @@ static int ibmvscsis_cap_mad(struct scsi_info *vscsi, struct iu_entry *iue)
>>  			 be64_to_cpu(mad->buffer),
>>  			 vscsi->dds.window[LOCAL].liobn, token);
>>  	if (rc == H_SUCCESS) {
>> -		strncpy(cap->name, dev_name(&vscsi->dma_dev->dev),
>> -			SRP_MAX_LOC_LEN);
>> +		strscpy_pad(cap->name, dev_name(&vscsi->dma_dev->dev),
>> +			sizeof(cap->name));
> 
> And this is a safe conversion to sizeof():
> 
> struct capabilities {
> 	...
>         char name[SRP_MAX_LOC_LEN];
> 
> 
> If we can convince ourselves that non of these are __nonstring types,
> then I think with the "info" change above, this should be good.
> 
> -Kees
>