Apply by doing:
	cd /usr/src/sys
	patch -p0 < bmap.patch

And then rebuild your kernel.

Index: ufs/ext2fs/ext2fs_bmap.c
===================================================================
RCS file: /cvs/src/sys/ufs/ext2fs/ext2fs_bmap.c,v
retrieving revision 1.3
retrieving revision 1.4
diff -u -r1.3 -r1.4
--- ufs/ext2fs/ext2fs_bmap.c	1997/06/12 21:09:31	1.3
+++ ufs/ext2fs/ext2fs_bmap.c	1999/04/25 00:36:46	1.4
@@ -120,7 +120,7 @@
 	struct ufsmount *ump;
 	struct mount *mp;
 	struct vnode *devvp;
-	struct indir a[NIADDR], *xap;
+	struct indir a[NIADDR+1], *xap;
 	daddr_t daddr;
 	long metalbn;
 	int error, maxrun = 0, num;
Index: ufs/ufs/ufs_bmap.c
===================================================================
RCS file: /cvs/src/sys/ufs/ufs/ufs_bmap.c,v
retrieving revision 1.4
retrieving revision 1.5
diff -u -r1.4 -r1.5
--- ufs/ufs/ufs_bmap.c	1997/05/30 08:35:02	1.4
+++ ufs/ufs/ufs_bmap.c	1999/04/25 00:36:47	1.5
@@ -114,7 +114,7 @@
 	struct ufsmount *ump;
 	struct mount *mp;
 	struct vnode *devvp;
-	struct indir a[NIADDR], *xap;
+	struct indir a[NIADDR+1], *xap;
 	daddr_t daddr;
 	long metalbn;
 #ifdef	TRACE
