nilfs2: add more check routines in mount process

nilfs2: Add more safeguard routines and protections in mount process,
which also makes nilfs2 report consistency error messages when
checkpoint number is invalid.
Signed-off-by: NZhu Yanhai <zhu.yanhai@gmail.com>
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

fs/nilfs2/cpfile.c

@@ -815,8 +815,10 @@ int nilfs_cpfile_is_snapshot(struct inode *cpfile, __u64 cno)
 	void *kaddr;
 	int ret;
 
-	if (cno == 0)
-		return -ENOENT; /* checkpoint number 0 is invalid */
+	/* CP number is invalid if it's zero or larger than the
+	largest	exist one.*/
+	if (cno == 0 || cno >= nilfs_mdt_cno(cpfile))
+		return -ENOENT;
 	down_read(&NILFS_MDT(cpfile)->mi_sem);
 
 	ret = nilfs_cpfile_get_checkpoint_block(cpfile, cno, 0, &bh);
@@ -824,6 +826,9 @@ int nilfs_cpfile_is_snapshot(struct inode *cpfile, __u64 cno)
 		goto out;
 	kaddr = kmap_atomic(bh->b_page, KM_USER0);
 	cp = nilfs_cpfile_block_get_checkpoint(cpfile, cno, bh, kaddr);
+	if (nilfs_checkpoint_invalid(cp))
+		ret = -ENOENT;
+	else
 		ret = nilfs_checkpoint_snapshot(cp);
 	kunmap_atomic(kaddr, KM_USER0);
 	brelse(bh);

fs/nilfs2/super.c

@@ -792,10 +792,15 @@ nilfs_fill_super(struct super_block *sb, void *data, int silent,
 
 	if (sb->s_flags & MS_RDONLY) {
 		if (nilfs_test_opt(sbi, SNAPSHOT)) {
+			down_read(&nilfs->ns_segctor_sem);
 			err = nilfs_cpfile_is_snapshot(nilfs->ns_cpfile,
 						       sbi->s_snapshot_cno);
-			if (err < 0)
+			up_read(&nilfs->ns_segctor_sem);
+			if (err < 0) {
+				if (err == -ENOENT)
+					err = -EINVAL;
 				goto failed_sbi;
+			}
 			if (!err) {
 				printk(KERN_ERR
 				       "NILFS: The specified checkpoint is "