PR: 131341

Index: sys/ufs/ffs/ffs_vfsops.c
===================================================================
--- sys/ufs/ffs/ffs_vfsops.c	(revision 188710)
+++ sys/ufs/ffs/ffs_vfsops.c	(working copy)
@@ -684,6 +684,23 @@ ffs_mountfs(devvp, mp, td)
 		error = EINVAL;		/* XXX needs translation */
 		goto out;
 	}
+	/*
+	 * XXX: If fs->fs_fsbtodb is not based on DEV_BSIZE recalculate it.
+	 */
+	if (fs->fs_fsize / fsbtodb(fs, 1) != DEV_BSIZE) {
+		/* integer log2(fs->fs_fsize / DEV_BSIZE) */
+		fs->fs_fsbtodb = 0;
+		while (fs->fs_fsbtodb <= FS_MAXFSBTODB) {
+			if (fs->fs_fsize / fsbtodb(fs, 1) == DEV_BSIZE)
+				break;
+			fs->fs_fsbtodb++;
+		}
+		if (fs->fs_fsbtodb > FS_MAXFSBTODB ||
+		    fs->fs_fsize % DEV_BSIZE != 0) {
+			error = EINVAL;
+			goto out;
+		}
+	}
 	fs->fs_fmod = 0;
 	fs->fs_flags &= ~FS_INDEXDIRS;	/* no support for directory indicies */
 	fs->fs_flags &= ~FS_UNCLEAN;
Index: sys/ufs/ffs/fs.h
===================================================================
--- sys/ufs/ffs/fs.h	(revision 188710)
+++ sys/ufs/ffs/fs.h	(working copy)
@@ -506,6 +506,11 @@ struct cg {
 #define	dbtofsb(fs, b)	((b) >> (fs)->fs_fsbtodb)
 
 /*
+ * Theoretical maximum value for fs_fsbtodb field.
+ */
+#define FS_MAXFSBTODB	((sizeof(daddr_t) * /*CHAR_BIT*/ 8) - 1)
+
+/*
  * Cylinder group macros to locate things in cylinder groups.
  * They calc filesystem addresses of cylinder group data structures.
  */