[PATCH] xfs: don't expose misaligned extszinherit hints to userspace

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

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

Commit 603f000b15f2 changed xfs_ioctl_setattr_check_extsize to reject an
attempt to set an EXTSZINHERIT extent size hint on a directory with
RTINHERIT set if the hint isn't a multiple of the realtime extent size.
However, I have recently discovered that it is possible to change the
realtime extent size when adding a rt device to a filesystem, which
means that the existence of directories with misaligned inherited hints
is not an accident.

As a result, it's possible that someone could have set a valid hint and
added an rt volume with a different rt extent size, which invalidates
the ondisk hints.  After such a sequence, FSGETXATTR will report a
misaligned hint, which FSSETXATTR will trip over, causing confusion if
the user was doing the usual GET/SET sequence to change some other
attribute.  Change xfs_fill_fsxattr to omit the hint if it isn't aligned
properly.

Fixes: 603f000b15f2 ("xfs: validate extsz hints against rt extent size when rtinherit is set")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 fs/xfs/xfs_ioctl.c |   19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index cfc2e099d558..72441c7be644 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1065,7 +1065,24 @@ xfs_fill_fsxattr(
 
 	fileattr_fill_xflags(fa, xfs_ip2xflags(ip));
 
-	fa->fsx_extsize = XFS_FSB_TO_B(mp, ip->i_extsize);
+	if (ip->i_diflags & XFS_DIFLAG_EXTSIZE) {
+		fa->fsx_extsize = XFS_FSB_TO_B(mp, ip->i_extsize);
+	} else if (ip->i_diflags & XFS_DIFLAG_EXTSZINHERIT) {
+		/*
+		 * Don't let a misaligned extent size hint on a directory
+		 * escape to userspace if it won't pass the setattr checks
+		 * later.
+		 */
+		if ((ip->i_diflags & XFS_DIFLAG_RTINHERIT) &&
+		    ip->i_extsize % mp->m_sb.sb_rextsize > 0) {
+			fa->fsx_xflags &= ~(FS_XFLAG_EXTSIZE |
+					    FS_XFLAG_EXTSZINHERIT);
+			fa->fsx_extsize = 0;
+		} else {
+			fa->fsx_extsize = XFS_FSB_TO_B(mp, ip->i_extsize);
+		}
+	}
+
 	if (ip->i_diflags2 & XFS_DIFLAG2_COWEXTSIZE)
 		fa->fsx_cowextsize = XFS_FSB_TO_B(mp, ip->i_cowextsize);
 	fa->fsx_projid = ip->i_projid;