linux-hardening - Re: [PATCH] scsi: message: fusion: replace deprecated strncpy with strscpy

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Date: Mon, 2 Oct 2023 10:41:48 -0700
From: Kees Cook <keescook@...omium.org>
To: Justin Stitt <justinstitt@...gle.com>
Cc: Sathya Prakash <sathya.prakash@...adcom.com>,
	Sreekanth Reddy <sreekanth.reddy@...adcom.com>,
	Suganath Prabu Subramani <suganath-prabu.subramani@...adcom.com>,
	MPT-FusionLinux.pdl@...adcom.com, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] scsi: message: fusion: replace deprecated strncpy with
 strscpy_pad

On Wed, Sep 27, 2023 at 04:06:09AM +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.
> 
> Since all these structs are copied out to userspace let's keep them
> NUL-padded by using `strscpy_pad` which guarantees NUL-termination of
> the destination buffer while also providing the NUL-padding behavior
> that strncpy has.
> 
> Let's also opt to use the more idiomatic strscpy usage of:
> `dest, src, sizeof(dest)` in cases where the compiler can determine the
> size of the destination buffer. Do this for all cases of strscpy...() in
> this file.
> 
> To be abundantly sure we don't leak stack data out to user space let's
> also change a strscpy to strscpy_pad. This strscpy was introduced in
> Commit dbe37c71d1246ec2 ("scsi: message: fusion: Replace all
> non-returning strlcpy() with strscpy()")
> 
> Note that since we are creating these structs with a copy_from_user()
> and modifying fields and then copying back out to the user it is
> probably OK not to explicitly NUL-pad everything as any data leak is
> probably just data from the user themselves. If this is too eager, let's
> opt for `strscpy` which is still in the spirit of removing deprecated
> strncpy usage treewide.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Cc: Kees Cook <keescook@...omium.org>
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Agreed -- this looks more robust and readable. Thanks!

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

-- 
Kees Cook