f2fs: Add sanity_check_inode() function

This was done as part of commit 5d64600d "f2fs: avoid bug_on on
corrupted inode" upstream, but the specific check that commit added is
not applicable to 4.14.

Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

fs/f2fs/inode.c

@@ -180,6 +180,13 @@ void f2fs_inode_chksum_set(struct f2fs_sb_info *sbi, struct page *page)
 	ri->i_inode_checksum = cpu_to_le32(f2fs_inode_chksum(sbi, page));
 }
 
+static bool sanity_check_inode(struct inode *inode)
+{
+	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
+
+	return true;
+}
+
 static int do_read_inode(struct inode *inode)
 {
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
@@ -281,6 +288,10 @@ struct inode *f2fs_iget(struct super_block *sb, unsigned long ino)
 	ret = do_read_inode(inode);
 	if (ret)
 		goto bad_inode;
+	if (!sanity_check_inode(inode)) {
+		ret = -EINVAL;
+		goto bad_inode;
+	}
 make_now:
 	if (ino == F2FS_NODE_INO(sbi)) {
 		inode->i_mapping->a_ops = &f2fs_node_aops;