fix mprotect vma_wants_writenotify prot

Fix mprotect bug in recent commit 3ed75eb8f1cd89565966599c4f77d2edb086d5b0
(setup vma->vm_page_prot by vm_get_page_prot()): the vma_wants_writenotify
case was setting the same prot as when not.

Nothing wrong with the use of protection_map[] in mmap_region(),
but use vm_get_page_prot() there too in the same ~VM_SHARED way.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Coly Li <coyli@suse.de>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

@@ -1171,8 +1171,7 @@ munmap_back:
 	vm_flags = vma->vm_flags;
 
 	if (vma_wants_writenotify(vma))
-		vma->vm_page_prot =
-			protection_map[vm_flags & (VM_READ|VM_WRITE|VM_EXEC)];
+		vma->vm_page_prot = vm_get_page_prot(vm_flags & ~VM_SHARED);
 
 	if (!file || !vma_merge(mm, prev, addr, vma->vm_end,
 			vma->vm_flags, NULL, file, pgoff, vma_policy(vma))) {

mm/mprotect.c

@@ -194,7 +194,7 @@ success:
 	vma->vm_flags = newflags;
 	vma->vm_page_prot = vm_get_page_prot(newflags);
 	if (vma_wants_writenotify(vma)) {
-		vma->vm_page_prot = vm_get_page_prot(newflags);
+		vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
 		dirty_accountable = 1;
 	}