From: Kees Cook <keescook@chromium.org>
To: Justin Stitt <justinstitt@google.com>
Cc: Dan Williams <dan.j.williams@intel.com>,
Vishal Verma <vishal.l.verma@intel.com>,
Dave Jiang <dave.jiang@intel.com>,
Ira Weiny <ira.weiny@intel.com>,
nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH v2] nvdimm/btt: replace deprecated strncpy with strscpy
Date: Thu, 19 Oct 2023 17:18:41 -0700 [thread overview]
Message-ID: <202310191718.4F728D9@keescook> (raw)
In-Reply-To: <20231019-strncpy-drivers-nvdimm-btt-c-v2-1-366993878cf0@google.com>
On Thu, Oct 19, 2023 at 05:54:15PM +0000, Justin Stitt wrote:
> Found with grep.
>
> 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 super->signature to be NUL-terminated based on its usage with
> memcmp against a NUL-term'd buffer:
> btt_devs.c:
> 253 | if (memcmp(super->signature, BTT_SIG, BTT_SIG_LEN) != 0)
> btt.h:
> 13 | #define BTT_SIG "BTT_ARENA_INFO\0"
>
> NUL-padding is not required as `super` is already zero-allocated:
> btt.c:
> 985 | super = kzalloc(sizeof(struct btt_sb), GFP_NOIO);
> ... rendering any additional NUL-padding superfluous.
>
> 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 also use the more idiomatic strscpy usage of (dest, src,
> sizeof(dest)) instead of (dest, src, XYZ_LEN) for buffers that the
> compiler can determine the size of. This more tightly correlates the
> destination buffer to the amount of bytes copied.
>
> Side note, this pattern of memcmp() on two NUL-terminated strings should
> really be changed to just a strncmp(), if i'm not mistaken? I see
> multiple instances of this pattern in this system:
>
> | if (memcmp(super->signature, BTT_SIG, BTT_SIG_LEN) != 0)
> | return false;
>
> where BIT_SIG is defined (weirdly) as a double NUL-terminated string:
>
> | #define BTT_SIG "BTT_ARENA_INFO\0"
>
> 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>
Reviewed-by: Kees Cook <keescook@chromium.org>
--
Kees Cook
next prev parent reply other threads:[~2023-10-20 0:18 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-19 17:54 [PATCH v2] nvdimm/btt: replace deprecated strncpy with strscpy Justin Stitt
2023-10-20 0:18 ` Kees Cook [this message]
2023-11-30 22:01 ` Kees Cook
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