linux-kernel - Re: [PATCH v2] scsi: target: Replace strlcpy with strscpy

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Message-ID: <202308301537.88398E90BB@keescook>
Date:   Wed, 30 Aug 2023 15:38:53 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Azeem Shaikh <azeemshaikh38@...il.com>
Cc:     "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-hardening@...r.kernel.org, linux-scsi@...r.kernel.org,
        target-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] scsi: target: Replace strlcpy with strscpy

On Wed, Aug 30, 2023 at 09:07:24PM +0000, Azeem Shaikh wrote:
> strlcpy() reads the entire source buffer first.
> This read may exceed the destination size limit.
> This is both inefficient and can lead to linear read
> overflows if a source string is not NUL-terminated [1].
> In an effort to remove strlcpy() completely [2], replace
> strlcpy() here with strscpy().
> 
> Direct replacement is safe here since return value of -errno
> is used to check for truncation instead of sizeof(dest).
> 
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
> [2] https://github.com/KSPP/linux/issues/89
> 
> Signed-off-by: Azeem Shaikh <azeemshaikh38@...il.com>
> ---
> v2:
>  * Replace all instances of strlcpy in this file instead of just 1.
> 
> v1:
>  * https://lore.kernel.org/all/20230830200717.4129442-1-azeemshaikh38@gmail.com/
> 
>  drivers/target/target_core_configfs.c |   27 ++++++++++++---------------
>  1 file changed, 12 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/target/target_core_configfs.c b/drivers/target/target_core_configfs.c
> index 936e5ff1b209..10a22a428267 100644
> --- a/drivers/target/target_core_configfs.c
> +++ b/drivers/target/target_core_configfs.c
> @@ -1392,16 +1392,15 @@ static ssize_t target_wwn_vendor_id_store(struct config_item *item,
>  	/* +2 to allow for a trailing (stripped) '\n' and null-terminator */
>  	unsigned char buf[INQUIRY_VENDOR_LEN + 2];
>  	char *stripped = NULL;
> -	size_t len;
> +	ssize_t len;
>  	ssize_t ret;
> 
> -	len = strlcpy(buf, page, sizeof(buf));
> -	if (len < sizeof(buf)) {
> +	len = strscpy(buf, page, sizeof(buf));
> +	if (len > 0) {
>  		/* Strip any newline added from userspace. */
>  		stripped = strstrip(buf);
> -		len = strlen(stripped);
>  	}
> -	if (len > INQUIRY_VENDOR_LEN) {
> +	if (len < 0 || strlen(stripped) > INQUIRY_VENDOR_LEN) {
>  		pr_err("Emulated T10 Vendor Identification exceeds"
>  			" INQUIRY_VENDOR_LEN: " __stringify(INQUIRY_VENDOR_LEN)
>  			"\n");

I would find these more readable if the "len = strlen" were left and the
final "if" becomes:

	if (len < 0 || len > INQUIRY_VENDOR_LEN)

> @@ -1448,16 +1447,15 @@ static ssize_t target_wwn_product_id_store(struct config_item *item,
>  	/* +2 to allow for a trailing (stripped) '\n' and null-terminator */
>  	unsigned char buf[INQUIRY_MODEL_LEN + 2];
>  	char *stripped = NULL;
> -	size_t len;
> +	ssize_t len;
>  	ssize_t ret;
> 
> -	len = strlcpy(buf, page, sizeof(buf));
> -	if (len < sizeof(buf)) {
> +	len = strscpy(buf, page, sizeof(buf));
> +	if (len > 0) {
>  		/* Strip any newline added from userspace. */
>  		stripped = strstrip(buf);
> -		len = strlen(stripped);
>  	}
> -	if (len > INQUIRY_MODEL_LEN) {
> +	if (len < 0 || strlen(stripped) > INQUIRY_MODEL_LEN) {
>  		pr_err("Emulated T10 Vendor exceeds INQUIRY_MODEL_LEN: "
>  			 __stringify(INQUIRY_MODEL_LEN)
>  			"\n");
> @@ -1504,16 +1502,15 @@ static ssize_t target_wwn_revision_store(struct config_item *item,
>  	/* +2 to allow for a trailing (stripped) '\n' and null-terminator */
>  	unsigned char buf[INQUIRY_REVISION_LEN + 2];
>  	char *stripped = NULL;
> -	size_t len;
> +	ssize_t len;
>  	ssize_t ret;
> 
> -	len = strlcpy(buf, page, sizeof(buf));
> -	if (len < sizeof(buf)) {
> +	len = strscpy(buf, page, sizeof(buf));
> +	if (len > 0) {
>  		/* Strip any newline added from userspace. */
>  		stripped = strstrip(buf);
> -		len = strlen(stripped);
>  	}
> -	if (len > INQUIRY_REVISION_LEN) {
> +	if (len < 0 || strlen(stripped) > INQUIRY_REVISION_LEN) {
>  		pr_err("Emulated T10 Revision exceeds INQUIRY_REVISION_LEN: "
>  			 __stringify(INQUIRY_REVISION_LEN)
>  			"\n");
> --
> 2.42.0.283.g2d96d420d3-goog
> 
> 

-- 
Kees Cook