linux-kernel - Re: [PATCH] scsi: 3w-sas: replace deprecated strncpy with strscpy

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Date:   Tue, 24 Oct 2023 17:27:42 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Adam Radford <aradford@...il.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] scsi: 3w-sas: replace deprecated strncpy with strscpy

On Mon, Oct 23, 2023 at 07:50:57PM +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.
> 
> This pattern of strncpy(dest, src, strlen(src)) is extremely bug-prone.
> This pattern basically never results in NUL-terminated destination
> strings unless `dest` was zero-initialized. The current implementation
> may be accidentally correct as tw_dev is zero-allocated via:
> 
> 	host = scsi_host_alloc(&driver_template, sizeof(TW_Device_Extension));
>         ...
> 	tw_dev = shost_priv(host);
> 
> ... wherein scsi_host_alloc zero-allocates host:
> 
>         shost = kzalloc(sizeof(struct Scsi_Host) + privsize, GFP_KERNEL);
> 
> Also, further suggesting this change is worthwhile is another strscpy()
> usage in 32-9xxx.c:
> 
> 	strscpy(tw_dev->tw_compat_info.driver_version, TW_DRIVER_VERSION,
> 		sizeof(tw_dev->tw_compat_info.driver_version));
> 
> 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.
> 
> Let's not be accidentally correct, let's be definitely correct.
> 
> 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>

Looks legit.

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

-- 
Kees Cook