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Subject[PATCH 5/6] USB: check serial-number string after device reset
Date
From: Alan Stern <stern@rowland.harvard.edu>

This patch (as1048) extends the descriptor checking after a device is
reset. Now the SerialNumber string descriptor is compared to its old
value, in addition to the device and configuration descriptors.

As a consequence, the kmalloc() call in usb_string() is now on the
error-handling pathway for usb-storage. Hence its allocation type is
changed to GFO_NOIO.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
Documentation/usb/persist.txt | 8 ++--
drivers/usb/core/hub.c | 65 +++++++++++++++++++++++++++++++---------
drivers/usb/core/message.c | 2 +-
3 files changed, 55 insertions(+), 20 deletions(-)
diff --git a/Documentation/usb/persist.txt b/Documentation/usb/persist.txt
index bea58db..d56cb1a 100644
--- a/Documentation/usb/persist.txt
+++ b/Documentation/usb/persist.txt
@@ -136,10 +136,10 @@ aren't guaranteed to be 100% accurate.

If you replace one USB device with another of the same type (same
manufacturer, same IDs, and so on) there's an excellent chance the
-kernel won't detect the change. Serial numbers and other strings are
-not compared. In many cases it wouldn't help if they were, because
-manufacturers frequently omit serial numbers entirely in their
-devices.
+kernel won't detect the change. The serial number string and other
+descriptors are compared with the kernel's stored values, but this
+might not help since manufacturers frequently omit serial numbers
+entirely in their devices.

Furthermore it's quite possible to leave a USB device exactly the same
while changing its media. If you replace the flash memory card in a
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 277d4ec..545fa72 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -3011,16 +3011,36 @@ void usb_hub_cleanup(void)
usb_deregister(&hub_driver);
} /* usb_hub_cleanup() */

-static int config_descriptors_changed(struct usb_device *udev)
-{
- unsigned index;
- unsigned len = 0;
- struct usb_config_descriptor *buf;
+static int descriptors_changed(struct usb_device *udev,
+ struct usb_device_descriptor *old_device_descriptor)
+{
+ int changed = 0;
+ unsigned index;
+ unsigned serial_len = 0;
+ unsigned len;
+ unsigned old_length;
+ int length;
+ char *buf;
+
+ if (memcmp(&udev->descriptor, old_device_descriptor,
+ sizeof(*old_device_descriptor)) != 0)
+ return 1;
+
+ /* Since the idVendor, idProduct, and bcdDevice values in the
+ * device descriptor haven't changed, we will assume the
+ * Manufacturer and Product strings haven't changed either.
+ * But the SerialNumber string could be different (e.g., a
+ * different flash card of the same brand).
+ */
+ if (udev->serial)
+ serial_len = strlen(udev->serial) + 1;

+ len = serial_len;
for (index = 0; index < udev->descriptor.bNumConfigurations; index++) {
- if (len < le16_to_cpu(udev->config[index].desc.wTotalLength))
- len = le16_to_cpu(udev->config[index].desc.wTotalLength);
+ old_length = le16_to_cpu(udev->config[index].desc.wTotalLength);
+ len = max(len, old_length);
}
+
buf = kmalloc(len, GFP_NOIO);
if (buf == NULL) {
dev_err(&udev->dev, "no mem to re-read configs after reset\n");
@@ -3028,25 +3048,41 @@ static int config_descriptors_changed(struct usb_device *udev)
return 1;
}
for (index = 0; index < udev->descriptor.bNumConfigurations; index++) {
- int length;
- int old_length = le16_to_cpu(udev->config[index].desc.wTotalLength);
-
+ old_length = le16_to_cpu(udev->config[index].desc.wTotalLength);
length = usb_get_descriptor(udev, USB_DT_CONFIG, index, buf,
old_length);
- if (length < old_length) {
+ if (length != old_length) {
dev_dbg(&udev->dev, "config index %d, error %d\n",
index, length);
+ changed = 1;
break;
}
if (memcmp (buf, udev->rawdescriptors[index], old_length)
!= 0) {
dev_dbg(&udev->dev, "config index %d changed (#%d)\n",
- index, buf->bConfigurationValue);
+ index,
+ ((struct usb_config_descriptor *) buf)->
+ bConfigurationValue);
+ changed = 1;
break;
}
}
+
+ if (!changed && serial_len) {
+ length = usb_string(udev, udev->descriptor.iSerialNumber,
+ buf, serial_len);
+ if (length + 1 != serial_len) {
+ dev_dbg(&udev->dev, "serial string error %d\n",
+ length);
+ changed = 1;
+ } else if (memcmp(buf, udev->serial, length) != 0) {
+ dev_dbg(&udev->dev, "serial string changed\n");
+ changed = 1;
+ }
+ }
+
kfree(buf);
- return index != udev->descriptor.bNumConfigurations;
+ return changed;
}

/**
@@ -3119,8 +3155,7 @@ int usb_reset_device(struct usb_device *udev)
goto re_enumerate;

/* Device might have changed firmware (DFU or similar) */
- if (memcmp(&udev->descriptor, &descriptor, sizeof descriptor)
- || config_descriptors_changed (udev)) {
+ if (descriptors_changed(udev, &descriptor)) {
dev_info(&udev->dev, "device firmware changed\n");
udev->descriptor = descriptor; /* for disconnect() calls */
goto re_enumerate;
diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index fefb922..a45076e 100644
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -784,7 +784,7 @@ int usb_string(struct usb_device *dev, int index, char *buf, size_t size)
if (size <= 0 || !buf || !index)
return -EINVAL;
buf[0] = 0;
- tbuf = kmalloc(256, GFP_KERNEL);
+ tbuf = kmalloc(256, GFP_NOIO);
if (!tbuf)
return -ENOMEM;

--
1.5.4.3


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