scsi: fcoe: Use sysfs_match_string() over fcoe_parse_mode()

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. Also check explicitly if
ctlr->mode is equal to FIP_CONN_TYPE_UNKNOWN -- this is probably preferred
to "<=" as the behavior is more obvious while maintaining functionality.

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@vger.kernel.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
Link: https://lore.kernel.org/r/20231212-strncpy-drivers-scsi-fcoe-fcoe_sysfs-c-v2-1-1f2d6b2fc409@google.com
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

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);
+		ctlr->mode = sysfs_match_string(fip_conn_type_names, buf);
-		if (ctlr->mode == FIP_CONN_TYPE_UNKNOWN) {
+		if (ctlr->mode < 0 || ctlr->mode == FIP_CONN_TYPE_UNKNOWN) {
 			LIBFCOE_SYSFS_DBG(ctlr, "Unknown mode %s provided.\n",
 					  buf);
 			return -EINVAL;