Subject: [PATCH 3/4] xfs: flush page mappings as part of setting immutable
From:   "Darrick J. Wong" <darrick.wong@oracle.com>
To:     darrick.wong@oracle.com
Cc:     david@fromorbit.com, linux-xfs@vger.kernel.org, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
        linux-btrfs@vger.kernel.org
Date:   Sun, 07 Apr 2019 13:27:23 -0700
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In-Reply-To: <155466882175.633834.15261194784129614735.stgit@magnolia>
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From: Darrick J. Wong <darrick.wong@oracle.com>

The chattr manpage has this to say about immutable files:

"A file with the 'i' attribute cannot be modified: it cannot be deleted
or renamed, no link can be created to this file, most of the file's
metadata can not be modified, and the file can not be opened in write
mode."

This means that we need to flush the page cache when setting the
immutable flag so that all mappings will become read-only again and
therefore programs cannot continue to write to writable mappings.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/xfs/xfs_ioctl.c |   51 ++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 44 insertions(+), 7 deletions(-)


diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 91938c4f3c67..5a1b96dad901 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -998,6 +998,31 @@ xfs_diflags_to_linux(
 #endif
 }
 
+/*
+ * Lock the inode against file io and page faults, then flush all dirty pages
+ * and wait for writeback and direct IO operations to finish.  Returns with
+ * the relevant inode lock flags set in @join_flags.  Caller is responsible for
+ * unlocking even on error return.
+ */
+static int
+xfs_ioctl_setattr_flush(
+	struct xfs_inode	*ip,
+	int			*join_flags)
+{
+	struct inode		*inode = VFS_I(ip);
+
+	/* Already locked the inode from IO?  Assume we're done. */
+	if (((*join_flags) & (XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL)) ==
+			     (XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL))
+		return 0;
+
+	/* Lock and flush all mappings and IO in preparation for flag change */
+	*join_flags = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
+	xfs_ilock(ip, *join_flags);
+	inode_dio_wait(inode);
+	return filemap_write_and_wait(inode->i_mapping);
+}
+
 static int
 xfs_ioctl_setattr_xflags(
 	struct xfs_trans	*tp,
@@ -1092,25 +1117,22 @@ xfs_ioctl_setattr_dax_invalidate(
 	if (!(fa->fsx_xflags & FS_XFLAG_DAX) && !IS_DAX(inode))
 		return 0;
 
-	if (S_ISDIR(inode->i_mode))
+	if (!S_ISREG(inode->i_mode))
 		return 0;
 
 	/* lock, flush and invalidate mapping in preparation for flag change */
-	xfs_ilock(ip, XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL);
-	error = filemap_write_and_wait(inode->i_mapping);
+	error = xfs_ioctl_setattr_flush(ip, join_flags);
 	if (error)
 		goto out_unlock;
 	error = invalidate_inode_pages2(inode->i_mapping);
 	if (error)
 		goto out_unlock;
-
-	*join_flags = XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL;
 	return 0;
 
 out_unlock:
-	xfs_iunlock(ip, XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL);
+	xfs_iunlock(ip, *join_flags);
+	*join_flags = 0;
 	return error;
-
 }
 
 /*
@@ -1356,6 +1378,21 @@ xfs_ioctl_setattr(
 	if (code)
 		goto error_free_dquots;
 
+	/*
+	 * If we are trying to set immutable on a file then flush everything to
+	 * disk to force all writable memory mappings back through the
+	 * pagefault handler.
+	 */
+	if (S_ISREG(VFS_I(ip)->i_mode) && !IS_IMMUTABLE(VFS_I(ip)) &&
+	    (fa->fsx_xflags & FS_XFLAG_IMMUTABLE)) {
+		code = xfs_ioctl_setattr_flush(ip, &join_flags);
+		if (code) {
+			xfs_iunlock(ip, join_flags);
+			join_flags = 0;
+			goto error_free_dquots;
+		}
+	}
+
 	tp = xfs_ioctl_setattr_get_trans(ip, join_flags);
 	if (IS_ERR(tp)) {
 		code = PTR_ERR(tp);