[PATCH v2] staging: erofs: fix an error handling in erofs_readdir()

[Matthew Wilcox]

On Sun, Aug 18, 2019 at 10:32:45AM +0800, Gao Xiang wrote:
> On Sat, Aug 17, 2019 at 07:20:55PM -0700, Matthew Wilcox wrote:
> > On Sun, Aug 18, 2019 at 09:56:31AM +0800, Gao Xiang wrote:
> > > @@ -82,8 +82,12 @@ static int erofs_readdir(struct file *f, struct dir_context *ctx)
> > >  		unsigned int nameoff, maxsize;
> > >  
> > >  		dentry_page = read_mapping_page(mapping, i, NULL);
> > > -		if (IS_ERR(dentry_page))
> > > -			continue;
> > > +		if (IS_ERR(dentry_page)) {
> > > +			errln("fail to readdir of logical block %u of nid %llu",
> > > +			      i, EROFS_V(dir)->nid);
> > > +			err = PTR_ERR(dentry_page);
> > > +			break;
> > 
> > I don't think you want to use the errno that came back from
> > read_mapping_page() (which is, I think, always going to be -EIO).
> > Rather you want -EFSCORRUPTED, at least if I understand the recent
> > patches to ext2/ext4/f2fs/xfs/...
> 
> Thanks for your reply and noticing this. :)
> 
> Yes, as I talked with you about read_mapping_page() in a xfs related
> topic earlier, I think I fully understand what returns here.
> 
> I actually had some concern about that before sending out this patch.
> You know the status is
>    PG_uptodate is not set and PG_error is set here.
> 
> But we cannot know it is actually a disk read error or due to
> corrupted images (due to lack of page flags or some status, and
> I think it could be a waste of page structure space for such
> corrupted image or disk error)...
> 
> And some people also like propagate errors from insiders...
> (and they could argue about err = -EFSCORRUPTED as well..)
> 
> I'd like hear your suggestion about this after my words above?
> still return -EFSCORRUPTED?

I don't think it matters whether it's due to a disk error or a corrupted
image.  We can't read the directory entry, so we should probably return
-EFSCORRUPTED.  Thinking about it some more, read_mapping_page() can
also return -ENOMEM, so it should probably look something like this:

		err = 0;
		if (dentry_page == ERR_PTR(-ENOMEM))
			err = -ENOMEM;
		else if (IS_ERR(dentry_page)) {
			errln("fail to readdir of logical block %u of nid %llu",
			      i, EROFS_V(dir)->nid);
			err = -EFSCORRUPTED;
		}

		if (err)
			break;