f2fs: check lower bound nid value in check_nid_range

This patch add lower bound verification for nid in check_nid_range, so nids
reserved like 0, node, meta passed by caller could be checked there.

And then check_nid_range could be used in f2fs_nfs_get_inode for simplifying
code.
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -641,7 +641,8 @@ static inline void f2fs_unlock_all(struct f2fs_sb_info *sbi)
  */
 static inline int check_nid_range(struct f2fs_sb_info *sbi, nid_t nid)
 {
-	WARN_ON((nid >= NM_I(sbi)->max_nid));
+	if (unlikely(nid < F2FS_ROOT_INO(sbi)))
+		return -EINVAL;
 	if (unlikely(nid >= NM_I(sbi)->max_nid))
 		return -EINVAL;
 	return 0;

fs/f2fs/inode.c

@@ -78,6 +78,7 @@ static int do_read_inode(struct inode *inode)
 	if (check_nid_range(sbi, inode->i_ino)) {
 		f2fs_msg(inode->i_sb, KERN_ERR, "bad inode number: %lu",
 			 (unsigned long) inode->i_ino);
+		WARN_ON(1);
 		return -EINVAL;
 	}
 

fs/f2fs/super.c

@@ -689,9 +689,7 @@ static struct inode *f2fs_nfs_get_inode(struct super_block *sb,
 	struct f2fs_sb_info *sbi = F2FS_SB(sb);
 	struct inode *inode;
 
-	if (unlikely(ino < F2FS_ROOT_INO(sbi)))
-		return ERR_PTR(-ESTALE);
-	if (unlikely(ino >= NM_I(sbi)->max_nid))
+	if (check_nid_range(sbi, ino))
 		return ERR_PTR(-ESTALE);
 
 	/*