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Date:   Tue, 24 Oct 2023 11:08:19 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Justin Stitt <justinstitt@google.com>
Cc:     Alexandra Winter <wintera@linux.ibm.com>,
        Wenjia Zhang <wenjia@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        linux-s390@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] s390/qeth: replace deprecated strncpy with strscpy
Message-ID: <202310241029.3E4A634@keescook>
References: <20231023-strncpy-drivers-s390-net-qeth_core_main-c-v1-1-e7ce65454446@google.com>
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In-Reply-To: <20231023-strncpy-drivers-s390-net-qeth_core_main-c-v1-1-e7ce65454446@google.com>
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On Mon, Oct 23, 2023 at 07:39:39PM +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 new_entry->dbf_name to be NUL-terminated based on its use with
> strcmp():
> |       if (strcmp(entry->dbf_name, name) == 0) {
> 
> Moreover, NUL-padding is not required as new_entry is kzalloc'd just
> before this assignment:
> |       new_entry = kzalloc(sizeof(struct qeth_dbf_entry), GFP_KERNEL);
> 
> ... rendering any future NUL-byte assignments (like the ones strncpy()
> does) redundant.
> 
> 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.
> 
> 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>

struct qeth_dbf_entry {
        char dbf_name[DBF_NAME_LEN];

The sizeof() replace looks right to me.

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

-Kees

> ---
> Note: build-tested only.
> 
> Found with: $ rg "strncpy\("
> ---
>  drivers/s390/net/qeth_core_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/s390/net/qeth_core_main.c b/drivers/s390/net/qeth_core_main.c
> index cd783290bde5..6af2511e070c 100644
> --- a/drivers/s390/net/qeth_core_main.c
> +++ b/drivers/s390/net/qeth_core_main.c
> @@ -6226,7 +6226,7 @@ static int qeth_add_dbf_entry(struct qeth_card *card, char *name)
>  	new_entry = kzalloc(sizeof(struct qeth_dbf_entry), GFP_KERNEL);
>  	if (!new_entry)
>  		goto err_dbg;
> -	strncpy(new_entry->dbf_name, name, DBF_NAME_LEN);
> +	strscpy(new_entry->dbf_name, name, sizeof(new_entry->dbf_name));
>  	new_entry->dbf_info = card->debug;
>  	mutex_lock(&qeth_dbf_list_mutex);
>  	list_add(&new_entry->dbf_list, &qeth_dbf_list);
> 
> ---
> base-commit: 9c5d00cb7b6bbc5a7965d9ab7d223b5402d1f02c
> change-id: 20231023-strncpy-drivers-s390-net-qeth_core_main-c-0b0ee08672ec
> 
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
> 
> 

-- 
Kees Cook