[PATCH] ntfs: fix mmap_prepare writable check for shared mappings

[Namjae Jeon <linkinjeon@kernel.org>]

Linus pointed out that checking only VMA_WRITE_BIT is incorrect.
Private writable mappings (MAP_PRIVATE) set VM_WRITE but do not
write back to the filesystem. Also, mappings that can become
writable via mprotect() (VM_MAYWRITE) must be handled.

Use vma_desc_test_all(VMA_SHARED_BIT, VMA_MAYWRITE_BIT) instead,
which matches what other filesystems do.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
---
 fs/ntfs/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ntfs/file.c b/fs/ntfs/file.c
index f55f55d4ca9a..e0265a8825f2 100644
--- a/fs/ntfs/file.c
+++ b/fs/ntfs/file.c
@@ -650,7 +650,7 @@ static int ntfs_file_mmap_prepare(struct vm_area_desc *desc)
 	if (NInoCompressed(NTFS_I(inode)))
 		return -EOPNOTSUPP;
 
-	if (vma_desc_test(desc, VMA_WRITE_BIT)) {
+	if (vma_desc_test_all(desc, VMA_SHARED_BIT, VMA_MAYWRITE_BIT)) {
 		struct inode *inode = file_inode(file);
 		loff_t from, to;
 		int err;
-- 
2.25.1