linux-kernel - [PATCH 4.8 11/33] device-dax: fix private mapping restriction, permit read-only

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Date:   Tue, 13 Dec 2016 09:16:12 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
        Pawel Lebioda <pawel.lebioda@...el.com>,
        Hugh Dickins <hughd@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: [PATCH 4.8 11/33] device-dax: fix private mapping restriction, permit read-only

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Williams <dan.j.williams@...el.com>

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@...ux.intel.com>
Cc: Pawel Lebioda <pawel.lebioda@...el.com>
Fixes: 4cb19355ea19 ("device-dax: fail all private mapping attempts")
Reported-by: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/dax/dax.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -324,7 +324,7 @@ static int check_vma(struct dax_dev *dax
 		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;