[PATCH v3] ntfs: fix race between fallocate and mmap reads

[Hongling Zeng]

The fallocate implementation only takes invalidate_lock for punch hole,
collapse range, and insert range operations. For standard allocation modes
(mode == 0, FALLOC_FL_KEEP_SIZE), the lock is not held.

During ntfs_attr_fallocate(), new clusters are mapped to the runlist via
ntfs_attr_map_cluster() before being zeroed by ntfs_dio_zero_range(). This
creates a window where concurrent mmap page faults can read uninitialized
disk data.

Since mmap uses filemap_fault() which takes invalidate_lock in shared mode,
it can fault in pages during this window and expose old disk contents to
userspace. This is an information leak and data integrity issue.

Fix by taking invalidate_lock for all fallocate operations, not just for
punch/collapse/insert modes. This prevents concurrent page faults from
accessing unzeroed clusters during the allocation window.

Fixes: 495e90fa3348 ("ntfs: update attrib operations")
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Baolin Liu <liubaolin@xxxxxxxxxx>
Reviewed-by: Hyunchul Lee <hyc.lee@xxxxxxxxx>
Signed-off-by: Hongling Zeng <zenghongling@xxxxxxxxxx>
---
Change in v3:
 -Remove map_locked after fixing the pre-lock early exit.
---
 fs/ntfs/file.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/fs/ntfs/file.c b/fs/ntfs/file.c
index 88747217ba61..1969e4f444f7 100644
--- a/fs/ntfs/file.c
+++ b/fs/ntfs/file.c
@@ -1116,7 +1116,6 @@ static long ntfs_fallocate(struct file *file, int mode, loff_t offset, loff_t le
 	struct ntfs_volume *vol = ni->vol;
 	int err = 0;
 	loff_t old_size;
-	bool map_locked = false;
 
 	if (mode & ~(NTFS_FALLOC_FL_SUPPORTED))
 		return -EOPNOTSUPP;
@@ -1148,16 +1147,13 @@ static long ntfs_fallocate(struct file *file, int mode, loff_t offset, loff_t le
 
 	inode_lock(vi);
 	if (NInoCompressed(ni) || NInoEncrypted(ni) || NInoWofCompressed(ni)) {
-		err = -EOPNOTSUPP;
-		goto out;
+		inode_unlock(vi);
+		return -EOPNOTSUPP;
 	}
 
 	inode_dio_wait(vi);
-	if (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_COLLAPSE_RANGE |
-		    FALLOC_FL_INSERT_RANGE)) {
-		filemap_invalidate_lock(vi->i_mapping);
-		map_locked = true;
-	}
+	/* Take invalidate_lock for all fallocate operations to prevent races */
+	filemap_invalidate_lock(vi->i_mapping);
 
 	switch (mode & FALLOC_FL_MODE_MASK) {
 	case FALLOC_FL_ALLOCATE_RANGE:
@@ -1182,8 +1178,7 @@ static long ntfs_fallocate(struct file *file, int mode, loff_t offset, loff_t le
 
 	err = file_modified(file);
 out:
-	if (map_locked)
-		filemap_invalidate_unlock(vi->i_mapping);
+	filemap_invalidate_unlock(vi->i_mapping);
 	if (!err) {
 		if (mode == 0 && NInoNonResident(ni) &&
 		    offset > old_size) {
-- 
2.25.1