[bug report] fs: f2fs: integer overflow in f2fs_truncate_inode_blocks()

[Roman Smirnov]

Hello. 

There is a possible bug in f2fs_truncate_inode_blocks():

    if (err < 0 && err != -ENOENT)
    			goto fail;
        ...
        offset[1] = 0;
        offset[0]++;
        nofs += err;

If err = -ENOENT then nofs will sum with an error code,
which is strange behaviour. Also if nofs < ENOENT this will
cause an overflow. err will be equal to -ENOENT with the
following call stack:

truncate_nodes()
  f2fs_get_node_page()
     __get_node_page()
        read_node_page()

It looks like ENOENT processing is missing here. What can you
say about it? How can it be fixed?

Found by Linux Verification Center (linuxtesting.org) with the
Svace static analysis tool.