From: Dan Williams <dan.j.williams@intel.com>
Date: Wed, 7 Dec 2016 01:03:35 +0000 (-0800)
Subject: device-dax: fix private mapping restriction, permit read-only
X-Git-Tag: v4.8.15~23
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ac65fe0bbdea786f0a1b4e2229e15af697c5b01c;p=thirdparty%2Fkernel%2Fstable.git

device-dax: fix private mapping restriction, permit read-only

commit 325896ffdf90f7cbd59fb873b7ba20d60d1ddf3c upstream.

Hugh notes in response to commit 4cb19355ea19 "device-dax: fail all
private mapping attempts":

  "I think that is more restrictive than you intended: haven't tried, but I
  believe it rejects a PROT_READ, MAP_SHARED, O_RDONLY fd mmap, leaving no
  way to mmap /dev/dax without write permission to it."

Indeed it does restrict read-only mappings, switch to checking
VM_MAYSHARE, not VM_SHARED.

Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Pawel Lebioda <pawel.lebioda@intel.com>
Fixes: 4cb19355ea19 ("device-dax: fail all private mapping attempts")
Reported-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
index ff64313770bdd..4894199cebab3 100644
--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -324,7 +324,7 @@ static int check_vma(struct dax_dev *dax_dev, struct vm_area_struct *vma,
 		return -ENXIO;
 
 	/* prevent private mappings from being established */
-	if ((vma->vm_flags & VM_SHARED) != VM_SHARED) {
+	if ((vma->vm_flags & VM_MAYSHARE) != VM_MAYSHARE) {
 		dev_info(dev, "%s: %s: fail, attempted private mapping\n",
 				current->comm, func);
 		return -EINVAL;