libata: transport: Use scnprintf() for avoiding potential buffer overflow

Since snprintf() returns the would-be-output size instead of the
actual output size, the succeeding calls may go beyond the given
buffer limit. Fix it by replacing with scnprintf().

Signed-off-by: Takashi Iwai <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/ata/libata-transport.c

···
 {									\
 	struct ata_port *ap = transport_class_to_port(dev);		\
 									\
-	return snprintf(buf, 20, format_string, cast ap->field);	\
+	return scnprintf(buf, 20, format_string, cast ap->field);	\
 }
 
 #define ata_port_simple_attr(field, name, format_string, type)		\
···
 {									\
 	struct ata_device *ata_dev = transport_class_to_dev(dev);	\
 									\
-	return snprintf(buf, 20, format_string, cast ata_dev->field);	\
+	return scnprintf(buf, 20, format_string, cast ata_dev->field);	\
 }
 
 #define ata_dev_simple_attr(field, format_string, type)	\
···
 	if (ata_dev->class == ATA_DEV_PMP)
 		return 0;
 	for(i=0;i<ATA_ID_WORDS;i++)  {
-		written += snprintf(buf+written, 20, "%04x%c",
+		written += scnprintf(buf+written, 20, "%04x%c",
 				    ata_dev->id[i],
 				    ((i+1) & 7) ? ' ' : '\n');
 	}
···
 	if (ata_dev->class != ATA_DEV_PMP)
 		return 0;
 	for(i=0;i<SATA_PMP_GSCR_DWORDS;i++)  {
-		written += snprintf(buf+written, 20, "%08x%c",
+		written += scnprintf(buf+written, 20, "%08x%c",
 				    ata_dev->gscr[i],
 				    ((i+1) & 3) ? ' ' : '\n');
 	}
···
 	else
 		mode = "unqueued";
 
-	return snprintf(buf, 20, "%s\n", mode);
+	return scnprintf(buf, 20, "%s\n", mode);
 }
 
 static DEVICE_ATTR(trim, S_IRUGO, show_ata_dev_trim, NULL);