[stable 3.2-3.16] IB/security: Restrict use of the write() interface

[Ben Hutchings <ben@decadent.org.uk>]

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This commit should be included in all stable branches:

commit e6bd18f57aad1a2d1ef40e646d03ed0f2515c9e3
Author: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Date:   Sun Apr 10 19:13:13 2016 -0600

    IB/security: Restrict use of the write() interface

When backporting, please fold the following change to the ipath driver
into the patch.

Ben.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/drivers/infiniband/hw/ipath/ipath_file_ops.c
+++ b/drivers/infiniband/hw/ipath/ipath_file_ops.c
@@ -44,6 +44,8 @@
 #include <linux/cpu.h>
 #include <asm/pgtable.h>
 
+#include <rdma/ib.h>
+
 #include "ipath_kernel.h"
 #include "ipath_common.h"
 #include "ipath_user_sdma.h"
@@ -2239,6 +2241,9 @@ static ssize_t ipath_write(struct file *
 	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;

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