[PATCH 1/3] xfs: use vfs helper to update file attributes after fallocate

["Darrick J. Wong" <djwong@kernel.org>]

From: Darrick J. Wong <djwong@kernel.org>

In XFS, we always update the inode change and modification time when any
preallocation operation succeeds.  Furthermore, as various fallocate
modes can change the file contents (extending EOF, punching holes,
zeroing things, shifting extents), we should drop file privileges like
suid just like we do for a regular write().  There's already a VFS
helper that figures all this out for us, so use that.

The net effect of this is that we no longer drop suid/sgid if the caller
is root, but we also now drop file capabilities.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 fs/xfs/xfs_file.c |   20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)


diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 22ad207bedf4..3b0d026396e5 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1057,12 +1057,26 @@ xfs_file_fallocate(
 		}
 	}
 
+	/* Update [cm]time and drop file privileges like a regular write. */
+	error = file_modified(file);
+	if (error)
+		goto out_unlock;
+
+	/*
+	 * If we need to change the PREALLOC flag or flush the log, do so.
+	 * We already updated the timestamps and cleared the suid flags, so we
+	 * don't need to do that again.  This must be committed before the size
+	 * change so that we don't trim post-EOF preallocations.
+	 */
 	if (file->f_flags & O_DSYNC)
 		flags |= XFS_PREALLOC_SYNC;
+	if (flags) {
+		flags |= XFS_PREALLOC_INVISIBLE;
 
-	error = xfs_update_prealloc_flags(ip, flags);
-	if (error)
-		goto out_unlock;
+		error = xfs_update_prealloc_flags(ip, flags);
+		if (error)
+			goto out_unlock;
+	}
 
 	/* Change file size if needed */
 	if (new_size) {