Re: [PATCH v2] btrfs: fix fallocate to use file_modified to update permissions consistently

[David Sterba <dsterba@suse.cz>]

On Mon, Mar 14, 2022 at 10:55:32AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> Since the initial introduction of (posix) fallocate back at the turn of
> the century, it has been possible to use this syscall to change the
> user-visible contents of files.  This can happen by extending the file
> size during a preallocation, or through any of the newer modes (punch,
> zero range).  Because the call can be used to change file contents, we
> should treat it like we do any other modification to a file -- update
> the mtime, and drop set[ug]id privileges/capabilities.
> 
> The VFS function file_modified() does all this for us if pass it a
> locked inode, so let's make fallocate drop permissions correctly.
> 
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
> v2: move up file_modified to catch a case where we could modify file
> contents but fail on something else before we end up calling
> file_modified

Added to misc-next, thanks.