drivers/rapidio/rio_cm.c: prevent possible heap overwrite

In the Linux kernel, the following vulnerability has been resolved:

drivers/rapidio/rio_cm.c: prevent possible heap overwrite

In

riocm_cdev_ioctl(RIO_CM_CHAN_SEND)

-> cm_chan_msg_send()

-> riocm_ch_send()

cm_chan_msg_send() checks that userspace didn't send too much data but

riocm_ch_send() failed to check that userspace sent sufficient data. The

result is that riocm_ch_send() can write to fields in the rio_ch_chan_hdr

which were outside the bounds of the space which cm_chan_msg_send()

allocated.

Address this by teaching riocm_ch_send() to check that the entire

rio_ch_chan_hdr was copied in from userspace.