linux-kernel - Re: [PATCH] scsi: ibmvfc: replace deprecated strncpy with strscpy

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Message-ID: <202311301311.717549FB@keescook>
Date:   Thu, 30 Nov 2023 13:12:48 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Tyrel Datwyler <tyreld@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] scsi: ibmvfc: replace deprecated strncpy with strscpy

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@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Yeah, this conversion looks correct to me too.

Reviewed-by: Kees Cook <keescook@...omium.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@...gle.com>
> 

-- 
Kees Cook