linux-hardening - Re: [PATCH] scsi: fcoe: use sysfs_match_string over fcoe_parse

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Date: Tue, 12 Dec 2023 13:34:10 -0800
From: Kees Cook <keescook@...omium.org>
To: Justin Stitt <justinstitt@...gle.com>
Cc: Hannes Reinecke <hare@...e.de>,
	"James E.J. Bottomley" <jejb@...ux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Bart Van Assche <bvanassche@....org>, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] scsi: fcoe: use sysfs_match_string over fcoe_parse_mode

On Mon, Dec 11, 2023 at 08:06:28PM +0000, Justin Stitt wrote:
> Instead of copying @buf into a new buffer and carefully managing its
> newline/null-terminating status, we can just use sysfs_match_string()
> as it uses sysfs_streq() internally which handles newline/null-term:
> 
> |  /**
> |   * sysfs_streq - return true if strings are equal, modulo trailing newline
> |   * @s1: one string
> |   * @s2: another string
> |   *
> |   * This routine returns true iff two strings are equal, treating both
> |   * NUL and newline-then-NUL as equivalent string terminations.  It's
> |   * geared for use with sysfs input strings, which generally terminate
> |   * with newlines but are compared against values without newlines.
> |   */
> |  bool sysfs_streq(const char *s1, const char *s2)
> |  ...
> 
> Then entirely drop the now unused fcoe_parse_mode, being careful to
> change if condition from checking for FIP_CONN_TYPE_UNKNOWN to < 0 as
> sysfs_match_string can return -EINVAL.
> 
> To get the compiler not to complain, make fip_conn_type_names
> const char * const. Perhaps, this should also be done for
> fcf_state_names.
> 
> This also removes an instance of strncpy() which helps [1].
> 
> Link: https://github.com/KSPP/linux/issues/90 [1]
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
> Builds upon patch and feedback from [2]:
> 
> However, this is different enough to warrant its own patch and not be a
> continuation.
> 
> [2]: https://lore.kernel.org/all/9f38f4aa-c6b5-4786-a641-d02d8bd92f7f@acm.org/
> ---
>  drivers/scsi/fcoe/fcoe_sysfs.c | 26 ++++----------------------
>  1 file changed, 4 insertions(+), 22 deletions(-)

My favorite kind of insert/delete ratio! :)

> 
> diff --git a/drivers/scsi/fcoe/fcoe_sysfs.c b/drivers/scsi/fcoe/fcoe_sysfs.c
> index e17957f8085c..f9c5d00f658a 100644
> --- a/drivers/scsi/fcoe/fcoe_sysfs.c
> +++ b/drivers/scsi/fcoe/fcoe_sysfs.c
> @@ -10,6 +10,7 @@
>  #include <linux/kernel.h>
>  #include <linux/etherdevice.h>
>  #include <linux/ctype.h>
> +#include <linux/string.h>
>  
>  #include <scsi/fcoe_sysfs.h>
>  #include <scsi/libfcoe.h>
> @@ -214,25 +215,13 @@ static const char *get_fcoe_##title##_name(enum table_type table_key)	\
>  	return table[table_key];					\
>  }
>  
> -static char *fip_conn_type_names[] = {
> +static const char * const fip_conn_type_names[] = {
>  	[ FIP_CONN_TYPE_UNKNOWN ] = "Unknown",
>  	[ FIP_CONN_TYPE_FABRIC ]  = "Fabric",
>  	[ FIP_CONN_TYPE_VN2VN ]   = "VN2VN",
>  };
>  fcoe_enum_name_search(ctlr_mode, fip_conn_type, fip_conn_type_names)
>  
> -static enum fip_conn_type fcoe_parse_mode(const char *buf)
> -{
> -	int i;
> -
> -	for (i = 0; i < ARRAY_SIZE(fip_conn_type_names); i++) {
> -		if (strcasecmp(buf, fip_conn_type_names[i]) == 0)
> -			return i;
> -	}
> -
> -	return FIP_CONN_TYPE_UNKNOWN;
> -}
> -
>  static char *fcf_state_names[] = {
>  	[ FCOE_FCF_STATE_UNKNOWN ]      = "Unknown",
>  	[ FCOE_FCF_STATE_DISCONNECTED ] = "Disconnected",
> @@ -274,17 +263,10 @@ static ssize_t store_ctlr_mode(struct device *dev,
>  			       const char *buf, size_t count)
>  {
>  	struct fcoe_ctlr_device *ctlr = dev_to_ctlr(dev);
> -	char mode[FCOE_MAX_MODENAME_LEN + 1];
>  
>  	if (count > FCOE_MAX_MODENAME_LEN)
>  		return -EINVAL;
>  
> -	strncpy(mode, buf, count);
> -
> -	if (mode[count - 1] == '\n')
> -		mode[count - 1] = '\0';
> -	else
> -		mode[count] = '\0';
>  
>  	switch (ctlr->enabled) {
>  	case FCOE_CTLR_ENABLED:
> @@ -297,8 +279,8 @@ static ssize_t store_ctlr_mode(struct device *dev,
>  			return -ENOTSUPP;
>  		}
>  
> -		ctlr->mode = fcoe_parse_mode(mode);
> -		if (ctlr->mode == FIP_CONN_TYPE_UNKNOWN) {
> +		ctlr->mode = sysfs_match_string(fip_conn_type_names, buf);
> +		if (ctlr->mode < 0) {

I think this needs to include FIP_CONN_TYPE_UNKNOWN to keep the logic
the same? (i.e. it could match the string "Unknown", so it would return
the enum value for that, 0 in this case.)

Otherwise, yeah, this looks good.

-Kees

>  			LIBFCOE_SYSFS_DBG(ctlr, "Unknown mode %s provided.\n",
>  					  buf);
>  			return -EINVAL;
> 
> ---
> base-commit: bee0e7762ad2c6025b9f5245c040fcc36ef2bde8
> change-id: 20231024-strncpy-drivers-scsi-fcoe-fcoe_sysfs-c-0e1dffe82855
> 
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
> 
> 

-- 
Kees Cook