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

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Message-ID: <202403181442.1E78DAA4@keescook>
Date: Mon, 18 Mar 2024 14:42:53 -0700
From: Kees Cook <keescook@...omium.org>
To: Justin Stitt <justinstitt@...gle.com>
Cc: "Martin K. Petersen" <martin.petersen@...cle.com>,
	linux-scsi@...r.kernel.org, target-devel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] scsi: target: replace deprecated strncpy with strscpy

On Mon, Mar 18, 2024 at 09:32:01PM +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 db_root and db_root_stage to be NUL-terminated based on its
> immediate use with pr_debug which expects a C-string argument (%s).
> Moreover, it seems NUL-padding is not required.
> 
> 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.
> 
> Additionally, we should also change snprintf() to scnprintf().
> `read_bytes` may be improperly assigned as snprintf() does NOT return
> the number of bytes written into the destination buffer, rather it
> returns the number of bytes that COULD have been written to that buffer
> if it had ample space. Conversely, scnprintf() returns the actual number
> of bytes written into the destination buffer (except the NUL-byte). This
> essentially means the ``if (!read_bytes)`` was probably never a possible
> branch.
> 
> After these changes, this code is more self-describing since it uses
> string APIs that more accurately match the desired behavior.
> 
> 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>

Good catch on "read_bytes"!

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

-- 
Kees Cook