xfs: kill suid/sgid through the truncate path.

commit 2962f5a5 upstream.

XFS has failed to kill suid/sgid bits correctly when truncating
files of non-zero size since commit c4ed4243 ("xfs: split
xfs_setattr") introduced in the 3.1 kernel. Fix it.

Fix it.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

(cherry picked from commit 56c19e89)
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/xfs/xfs_iops.c

@@ -507,6 +507,28 @@ xfs_vn_getattr(
 	return 0;
 }
 
+static void
+xfs_setattr_mode(
+	struct xfs_trans	*tp,
+	struct xfs_inode	*ip,
+	struct iattr		*iattr)
+{
+	struct inode	*inode = VFS_I(ip);
+	umode_t		mode = iattr->ia_mode;
+
+	ASSERT(tp);
+	ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
+
+	if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
+		mode &= ~S_ISGID;
+
+	ip->i_d.di_mode &= S_IFMT;
+	ip->i_d.di_mode |= mode & ~S_IFMT;
+
+	inode->i_mode &= S_IFMT;
+	inode->i_mode |= mode & ~S_IFMT;
+}
+
 int
 xfs_setattr_nonsize(
 	struct xfs_inode	*ip,
@@ -658,18 +680,8 @@ xfs_setattr_nonsize(
 	/*
 	 * Change file access modes.
 	 */
-	if (mask & ATTR_MODE) {
-		umode_t mode = iattr->ia_mode;
-
-		if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
-			mode &= ~S_ISGID;
-
-		ip->i_d.di_mode &= S_IFMT;
-		ip->i_d.di_mode |= mode & ~S_IFMT;
-
-		inode->i_mode &= S_IFMT;
-		inode->i_mode |= mode & ~S_IFMT;
-	}
+	if (mask & ATTR_MODE)
+		xfs_setattr_mode(tp, ip, iattr);
 
 	/*
 	 * Change file access or modified times.
@@ -768,9 +780,8 @@ xfs_setattr_size(
 		return XFS_ERROR(error);
 
 	ASSERT(S_ISREG(ip->i_d.di_mode));
-	ASSERT((mask & (ATTR_MODE|ATTR_UID|ATTR_GID|ATTR_ATIME|ATTR_ATIME_SET|
-			ATTR_MTIME_SET|ATTR_KILL_SUID|ATTR_KILL_SGID|
-			ATTR_KILL_PRIV|ATTR_TIMES_SET)) == 0);
+	ASSERT((mask & (ATTR_UID|ATTR_GID|ATTR_ATIME|ATTR_ATIME_SET|
+			ATTR_MTIME_SET|ATTR_KILL_PRIV|ATTR_TIMES_SET)) == 0);
 
 	lock_flags = XFS_ILOCK_EXCL;
 	if (!(flags & XFS_ATTR_NOLOCK))
@@ -902,6 +913,12 @@ xfs_setattr_size(
 		xfs_iflags_set(ip, XFS_ITRUNCATED);
 	}
 
+	/*
+	 * Change file access modes.
+	 */
+	if (mask & ATTR_MODE)
+		xfs_setattr_mode(tp, ip, iattr);
+
 	if (mask & ATTR_CTIME) {
 		inode->i_ctime = iattr->ia_ctime;
 		ip->i_d.di_ctime.t_sec = iattr->ia_ctime.tv_sec;