RDMA/ionic: bound node_desc sysfs read with %.64s

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

RDMA/ionic: bound node_desc sysfs read with %.64s

node_desc[64] in struct ib_device is not guaranteed to be NUL-
terminated. The core IB sysfs handler uses "%.64s" for exactly this
reason (drivers/infiniband/core/sysfs.c:1307), since node_desc_store()
performs a raw memcpy of up to IB_DEVICE_NODE_DESC_MAX bytes with no NUL
termination:

memcpy(desc.node_desc, buf, min_t(int, count, IB_DEVICE_NODE_DESC_MAX));

If exactly 64 bytes are written via the node_desc sysfs file, the array
contains no NUL byte. The ionic hca_type_show() handler uses unbounded
"%s" and will read past the end of node_desc into adjacent fields of
struct ib_device until it encounters a NUL.

ionic supports IB_DEVICE_MODIFY_NODE_DESC, so this is triggerable by
userspace.

Match the core handler and bound the format specifier.