ALSA: firewire-lib/bebob/oxfw: improve response evaluation for AV/C commands

In ALSA firewire stack, some AV/C commands are supported, including
vendor's extensions. Drivers includes response parser of each command,
according to its requirements, while the parser is written with loose
fashion in two points; error check and length check. This doesn't cause
any issues such as kernel corruption, but should be improved.

This commit modifies evaluations of return value on each parsers.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/fcp.c

@@ -63,7 +63,9 @@ int avc_general_set_sig_fmt(struct fw_unit *unit, unsigned int rate,
 	/* do transaction and check buf[1-5] are the same against command */
 	err = fcp_avc_transaction(unit, buf, 8, buf, 8,
 				  BIT(1) | BIT(2) | BIT(3) | BIT(4) | BIT(5));
-	if (err >= 0 && err < 8)
+	if (err < 0)
+		;
+	else if (err < 8)
 		err = -EIO;
 	else if (buf[0] == 0x08) /* NOT IMPLEMENTED */
 		err = -ENOSYS;
@@ -106,7 +108,9 @@ int avc_general_get_sig_fmt(struct fw_unit *unit, unsigned int *rate,
 	/* do transaction and check buf[1-4] are the same against command */
 	err = fcp_avc_transaction(unit, buf, 8, buf, 8,
 				  BIT(1) | BIT(2) | BIT(3) | BIT(4));
-	if (err >= 0 && err < 8)
+	if (err < 0)
+		;
+	else if (err < 8)
 		err = -EIO;
 	else if (buf[0] == 0x08) /* NOT IMPLEMENTED */
 		err = -ENOSYS;
@@ -154,7 +158,9 @@ int avc_general_get_plug_info(struct fw_unit *unit, unsigned int subunit_type,
 	buf[3] = 0xff & subfunction;
 
 	err = fcp_avc_transaction(unit, buf, 8, buf, 8, BIT(1) | BIT(2));
-	if (err >= 0 && err < 8)
+	if (err < 0)
+		;
+	else if (err < 8)
 		err = -EIO;
 	else if (buf[0] == 0x08) /* NOT IMPLEMENTED */
 		err = -ENOSYS;