ipath: Restrict use of the write() interface

BugLink: http://bugs.launchpad.net/bugs/1614560

Commit e6bd18f5 ("IB/security: Restrict use of the write()
interface") fixed a security problem with various write()
implementations in the Infiniband subsystem.  In older kernel versions
the ipath_write() function has the same problem and needs the same
restriction.  (The ipath driver has been completely removed upstream.)
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/staging/rdma/ipath/ipath_file_ops.c

@@ -45,6 +45,8 @@
 #include <linux/uio.h>
 #include <asm/pgtable.h>
 
+#include <rdma/ib.h>
+
 #include "ipath_kernel.h"
 #include "ipath_common.h"
 #include "ipath_user_sdma.h"
@@ -2243,6 +2245,9 @@ static ssize_t ipath_write(struct file *fp, const char __user *data,
 	ssize_t ret = 0;
 	void *dest;
 
+	if (WARN_ON_ONCE(!ib_safe_file_access(fp)))
+		return -EACCES;
+
 	if (count < sizeof(cmd.type)) {
 		ret = -EINVAL;
 		goto bail;