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

From: Greg Kroah-Hartman
Date: Tue Dec 13 2016 - 12:19:58 EST

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


From: Dan Williams <dan.j.williams@xxxxxxxxx>

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

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

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;