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

Hugh notes in response to commit 4cb1935 "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: <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Pawel Lebioda <[email protected]> Fixes: 4cb1935 ("device-dax: fail all private mapping attempts") Reported-by: Hugh Dickins <[email protected]> Signed-off-by: Dan Williams <[email protected]>
zuai · Dec 7, 2016 · 325896f · 325896f
1 parent a7de92d
commit 325896f
Showing 1 changed file with 1 addition and 1 deletion.
diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
@@ -271,7 +271,7 @@ 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;