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Date:   Tue, 12 Dec 2023 13:23:01 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Justin Stitt <justinstitt@google.com>
Cc:     Michael Cyr <mikecyr@linux.ibm.com>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        linux-scsi@vger.kernel.org, target-devel@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH v2] scsi: ibmvscsi_tgt: replace deprecated strncpy with
 strscpy
Message-ID: <202312121321.E15E09BF@keescook>
References: <20231212-strncpy-drivers-scsi-ibmvscsi_tgt-ibmvscsi_tgt-c-v2-1-bdb9a7cd96c8@google.com>
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In-Reply-To: <20231212-strncpy-drivers-scsi-ibmvscsi_tgt-ibmvscsi_tgt-c-v2-1-bdb9a7cd96c8@google.com>
Precedence: bulk

On Tue, Dec 12, 2023 at 01:20:20AM +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.
> 
> However, for cap->name and info let's use strscpy_pad as they are
> allocated via dma_alloc_coherent():
> |       cap = dma_alloc_coherent(&vscsi->dma_dev->dev, olen, &token,
> |                                GFP_ATOMIC);
> &
> |       info = dma_alloc_coherent(&vscsi->dma_dev->dev, sizeof(*info), &token,
> |                                 GFP_ATOMIC);
> 
> 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>

This looks good to me. The only question that I haven't seen an answer
to from the maintainers is whether this is a __nonstring or not. It
really looks like it should be a C String, so with that assumption:

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

-Kees

-- 
Kees Cook