linux_usbfs: Fix parsing of descriptors for multi-configuration devices

Commit e2be556 ("linux_usbfs: Parse config descriptors during device
initialization") introduced a regression for devices with multiple
configurations. The logic that verifies the reported length of the
configuration descriptors failed to count the length of the
configuration descriptor itself and would truncate the actual length by
9 bytes, leading to a parsing error for subsequent descriptors.

Closes #825

Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>

libusb/os/linux_usbfs.c

@@ -641,7 +641,12 @@ static int seek_to_next_config(struct libusb_context *ctx,
 	uint8_t *buffer, size_t len)
 {
 	struct usbi_descriptor_header *header;
-	int offset = 0;
+	int offset;
+
+	/* Start seeking past the config descriptor */
+	offset = LIBUSB_DT_CONFIG_SIZE;
+	buffer += LIBUSB_DT_CONFIG_SIZE;
+	len -= LIBUSB_DT_CONFIG_SIZE;
 
 	while (len > 0) {
 		if (len < 2) {
@@ -718,7 +723,7 @@ static int parse_config_descriptors(struct libusb_device *dev)
 		}
 
 		if (priv->sysfs_dir) {
-			 /*
+			/*
 			 * In sysfs wTotalLength is ignored, instead the kernel returns a
 			 * config descriptor with verified bLength fields, with descriptors
 			 * with an invalid bLength removed.
@@ -727,8 +732,7 @@ static int parse_config_descriptors(struct libusb_device *dev)
 			int offset;
 
 			if (num_configs > 1 && idx < num_configs - 1) {
-				offset = seek_to_next_config(ctx, buffer + LIBUSB_DT_CONFIG_SIZE,
-							     remaining - LIBUSB_DT_CONFIG_SIZE);
+				offset = seek_to_next_config(ctx, buffer, remaining);
 				if (offset < 0)
 					return offset;
 				sysfs_config_len = (uint16_t)offset;

libusb/version_nano.h

@@ -1 +1 @@
-#define LIBUSB_NANO 11585
+#define LIBUSB_NANO 11586