Commit 77b0a09967 ("cdc-ncm: use common parser") added a dangerous
new trust in the CDC functional descriptors presented by the device,
unconditionally assuming that any device handled by the driver has
a CDC Union descriptor.
This descriptor is required by the NCM and MBIM specs, but crashing
on non-compliant devices is still unacceptable. Not only will that
allow malicious devices to crash the kernel, but in this case it is
also well known that there are non-compliant real devices on the
market - as shown by the comment accompanying the IAD workaround
in the same function.
The Sierra Wireless EM7305 is an example of such device, having
a CDC header and a CDC MBIM descriptor but no CDC Union:
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 12
bAlternateSetting 0
bNumEndpoints 1
bInterfaceClass 2 Communications
bInterfaceSubClass 14
bInterfaceProtocol 0
iInterface 0
CDC Header:
bcdCDC 1.10
CDC MBIM:
bcdMBIMVersion 1.00
wMaxControlMessage 4096
bNumberFilters 16
bMaxFilterSize 128
wMaxSegmentSize 4064
bmNetworkCapabilities 0x20
8-byte ntb input size
Endpoint Descriptor:
..
The conversion to a common parser also left the local cdc_union
variable untouched. This caused the IAD workaround code to be applied
to all devices with an IAD descriptor, which was never intended. Finish
the conversion by testing for hdr.usb_cdc_union_desc instead.
Cc: Oliver Neukum <oneukum@suse.com>
Fixes: 77b0a09967 ("cdc-ncm: use common parser")
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>
6527f833bf