Re: [PATCH v2] ntfs: fix race between fallocate and mmap reads

[Hongling Zeng <zhongling0719@126.com>]

Hi Hyunchul,

Thanks for the review.

I sent an updated patch too quickly. Simply removing map_locked is not
correct because there is an early compressed-file exit before
invalidate_lock is taken, so making the unlock path unconditional would
unbalance the locking.

Please ignore the previous version. I'll send a v3 with the control-flow
fix shortly.

Thanks,
Hongling
在 2026年08月27日 11:16, Hongling Zeng 写道:
> 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@vger.kernel.org
> Signed-off-by: Hongling Zeng <zenghongling@kylinos.cn>
> Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
> Reviewed-by: Baolin Liu <liubaolin@kylinos.cn>
> ---
> Change in v2:
>   -Remove now-unnecessary map_locked variable.
> ---
>   fs/ntfs/file.c | 7 ++-----
>   1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/fs/ntfs/file.c b/fs/ntfs/file.c
> index 88747217ba61..779baafa0319 100644
> --- a/fs/ntfs/file.c
> +++ b/fs/ntfs/file.c
> @@ -1153,11 +1153,8 @@ static long ntfs_fallocate(struct file *file, int mode, loff_t offset, loff_t le
>   	}
>   
>   	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: