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Date: Thu, 18 Jan 2024 14:43:16 -0800
From: Kees Cook <keescook@chromium.org>
To: Tyrel Datwyler <turtle.in.the.kernel@gmail.com>
Cc: Justin Stitt <justinstitt@google.com>,
	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: <202401181442.ABC133B203@keescook>
References: <20231212-strncpy-drivers-scsi-ibmvscsi_tgt-ibmvscsi_tgt-c-v2-1-bdb9a7cd96c8@google.com>
 <202312121321.E15E09BF@keescook>
 <9f246fbc-b2e4-4585-912d-a5a00ac8cd04@gmail.com>
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In-Reply-To: <9f246fbc-b2e4-4585-912d-a5a00ac8cd04@gmail.com>

On Thu, Jan 18, 2024 at 12:21:04PM -0800, Tyrel Datwyler wrote:
> On 12/12/23 13:23, Kees Cook wrote:
> > 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:
> 
> To reaffirm the assumption, as I mentioned in my response to v1 these are
> intended to be handled as C strings.

Great; thanks! Are you taking this, or should I carry it in the
hardening tree?

-Kees

> 
> Acked-by: Tyrel Datwyler <tyreld@linux.ibm.com>
> 
> > 
> > Reviewed-by: Kees Cook <keescook@chromium.org>
> > 
> > -Kees
> > 
> 

-- 
Kees Cook