https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=238412
Bug ID: 238412
Summary: libusb_get_config_descriptor() should return
LIBUSB_NOT_FOUND on out-of-range config_index
Product: Base System
Version: 11.3-STABLE
Hardware: Any
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: usb
Assignee: [email protected]
Reporter: [email protected]
Created attachment 204897
--> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=204897&action=edit
proposed patch
libusb_get_config_descriptor() in FreeBSD issues a get_config_descriptor
request even if the config_index argument is out of range. On the other
hand, the function in Linux checks the config_index argument against
bNumConfigurations in the device descriptor and returns LIBUSB_ERROR_NOT_FOUND
without issuing get_config_descriptor requests.
It seems that get_config_descriptor requests with invalid config_index
values for most USB devices fail, but there is a device (USB DrDAQ from
Pico Technology) that does not check the config_index value. The request
for USB DrDAQ succeeds even if the config_index value is invalid.
As a result, the behavior of libusb_get_config_descriptor() in FreeBSD
differs from the one in Linux on such a device.
This makes qemu hang on FreeBSD with USB passthrough enabled because qemu
repeats libusb_get_config_descriptor() with incrementing config_index until
the function returns an error.
The specification of libusb_get_config_descriptor():
http://libusb.sourceforge.net/api-1.0/group__libusb__desc.html#gaa635d9aec77d\e4895dd0896ccf001532
The implementation in Linux:
https://github.com/libusb/libusb/blob/v1.0.22/libusb/descriptor.c#L625
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