scsi: ibmvfc: replace deprecated strncpy with strscpy

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 expect these fields to be NUL-terminated as the property names from
which they are derived are also NUL-terminated.

Moreover, NUL-padding is not required as our destination buffers are
already NUL-allocated and any future NUL-byte assignments are redundant
(like the ones that strncpy() does).
ibmvfc_probe() ->
|       struct ibmvfc_host *vhost;
|       struct Scsi_Host *shost;
...
| 	shost = scsi_host_alloc(&driver_template, sizeof(*vhost));
... **side note: is this a bug? Looks like a type to me   ^^^^^**
...
|	vhost = shost_priv(shost);

... where shost_priv() is:
|       static inline void *shost_priv(struct Scsi_Host *shost)
|       {
|       	return (void *)shost->hostdata;
|       }

.. and:
scsi_host_alloc() ->
| 	shost = kzalloc(sizeof(struct Scsi_Host) + privsize, GFP_KERNEL);

And for login_info->..., NUL-padding is also not required as it is
explicitly memset to 0:
|	memset(login_info, 0, sizeof(*login_info));

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.

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@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 drivers/scsi/ibmvscsi/ibmvfc.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)


---
base-commit: ffc253263a1375a65fa6c9f62a893e9767fbebfa
change-id: 20231030-strncpy-drivers-scsi-ibmvscsi-ibmvfc-c-ccfce3255d58

Best regards,
--
Justin Stitt <justinstitt@google.com>

On Mon, Oct 30, 2023 at 07:04:33PM +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 expect these fields to be NUL-terminated as the property names from
> which they are derived are also NUL-terminated.
> 
> Moreover, NUL-padding is not required as our destination buffers are
> already NUL-allocated and any future NUL-byte assignments are redundant
> (like the ones that strncpy() does).
> ibmvfc_probe() ->
> |       struct ibmvfc_host *vhost;
> |       struct Scsi_Host *shost;
> ...
> | 	shost = scsi_host_alloc(&driver_template, sizeof(*vhost));
> ... **side note: is this a bug? Looks like a type to me   ^^^^^**

I think this is the "privsize", so *vhost is correct, IIUC.

> ...
> |	vhost = shost_priv(shost);

I.e. vhost is a part of the shost allocation

> 
> ... where shost_priv() is:
> |       static inline void *shost_priv(struct Scsi_Host *shost)
> |       {
> |       	return (void *)shost->hostdata;
> |       }
> 
> .. and:
> scsi_host_alloc() ->
> | 	shost = kzalloc(sizeof(struct Scsi_Host) + privsize, GFP_KERNEL);

As seen here. :)

> 
> And for login_info->..., NUL-padding is also not required as it is
> explicitly memset to 0:
> |	memset(login_info, 0, sizeof(*login_info));
> 
> 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.
> 
> 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@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Yeah, this conversion looks correct to me too.

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
> Note: build-tested only.
> 
> Found with: $ rg "strncpy\("
> ---
>  drivers/scsi/ibmvscsi/ibmvfc.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/scsi/ibmvscsi/ibmvfc.c b/drivers/scsi/ibmvscsi/ibmvfc.c
> index ce9eb00e2ca0..e73a39b1c832 100644
> --- a/drivers/scsi/ibmvscsi/ibmvfc.c
> +++ b/drivers/scsi/ibmvscsi/ibmvfc.c
> @@ -1455,7 +1455,7 @@ static void ibmvfc_gather_partition_info(struct ibmvfc_host *vhost)
>  
>  	name = of_get_property(rootdn, "ibm,partition-name", NULL);
>  	if (name)
> -		strncpy(vhost->partition_name, name, sizeof(vhost->partition_name));
> +		strscpy(vhost->partition_name, name, sizeof(vhost->partition_name));
>  	num = of_get_property(rootdn, "ibm,partition-no", NULL);
>  	if (num)
>  		vhost->partition_number = *num;
> @@ -1498,13 +1498,15 @@ static void ibmvfc_set_login_info(struct ibmvfc_host *vhost)
>  	login_info->async.va = cpu_to_be64(vhost->async_crq.msg_token);
>  	login_info->async.len = cpu_to_be32(async_crq->size *
>  					    sizeof(*async_crq->msgs.async));
> -	strncpy(login_info->partition_name, vhost->partition_name, IBMVFC_MAX_NAME);
> -	strncpy(login_info->device_name,
> -		dev_name(&vhost->host->shost_gendev), IBMVFC_MAX_NAME);
> +	strscpy(login_info->partition_name, vhost->partition_name,
> +		sizeof(login_info->partition_name));
> +
> +	strscpy(login_info->device_name,
> +		dev_name(&vhost->host->shost_gendev), sizeof(login_info->device_name));
>  
>  	location = of_get_property(of_node, "ibm,loc-code", NULL);
>  	location = location ? location : dev_name(vhost->dev);
> -	strncpy(login_info->drc_name, location, IBMVFC_MAX_NAME);
> +	strscpy(login_info->drc_name, location, sizeof(login_info->drc_name));
>  }
>  
>  /**
> 
> ---
> base-commit: ffc253263a1375a65fa6c9f62a893e9767fbebfa
> change-id: 20231030-strncpy-drivers-scsi-ibmvscsi-ibmvfc-c-ccfce3255d58
> 
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
>

On Mon, 30 Oct 2023 19:04:33 +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 expect these fields to be NUL-terminated as the property names from
> which they are derived are also NUL-terminated.
> 
> [...]

Applied to 6.8/scsi-queue, thanks!

[1/1] scsi: ibmvfc: replace deprecated strncpy with strscpy
      https://git.kernel.org/mkp/scsi/c/a9baa16b4fc1