omfs: refuse to mount if bitmap pointer is obviously wrong

If the free space bitmap pointer is corrupted such that it lies outside
of the number of blocks in the filesystem, print a message and fail the
mount so the user can fix it offline.

Signed-off-by: Bob Copeland <me@bobcopeland.com>

fs/omfs/inode.c

@@ -509,6 +509,15 @@ static int omfs_fill_super(struct super_block *sb, void *data, int silent)
 		goto out_brelse_bh2;
 	}
 
+	if (sbi->s_bitmap_ino != ~0ULL &&
+	    sbi->s_bitmap_ino > sbi->s_num_blocks) {
+		printk(KERN_ERR "omfs: free space bitmap location is corrupt "
+			"(%llx, total blocks %llx)\n",
+			(unsigned long long) sbi->s_bitmap_ino,
+			(unsigned long long) sbi->s_num_blocks);
+		goto out_brelse_bh2;
+	}
+
 	ret = omfs_get_imap(sb);
 	if (ret)
 		goto out_brelse_bh2;