On Wed, Sep 23, 2020 at 1:44 AM Pavel Machek <pavel@xxxxxxx> wrote: > > > > > https://www.openwall.com/lists/oss-security/2020/09/15/2 > > Thank you for the pointer! Note that for me to be willing to take the softscollback code back, it really would have to be more than just a revert and a trivial fix. It would have to be more along the lines of "this is simplified and verified". For example, at a minimum all the VT_RESIZE etc stuff would have to clearly and obviously reset the soft-scrollback, so that we simply can't have those kinds of issues. If you look at that commit 50145474f6ef ("fbcon: remove soft scrollback code") that removes the code, most of that code really doesn't make much sense. I dare anybody looking at that removed fbcon_redraw_softback() function (or the different cases in fbcon_scrolldelta(), for that matter) to claim they understand what it is doing. It's very odd code, and it handles a lot of odd special cases. So I wouldn't mind re-introducing the scrollback code, but the reintroduced version needs to be simple and fairly _obvious_. It would need to not have all those odd special cases, and it would need to clearly not have any subtle issues with things like font or screen resizing. I'd also suggest that it not even try to handle the multiple virtual console case. And yes, some of it may involve also clarifying the code in the VT code itself, so that the interactions with the cursor and VT switching is more obvious. Maybe instead of trying to deal with a SW cursor when scrollback is active, just hide the cursor entirely before doing scrollback. And make change_console (and all the resizing) explicitly reset scrollback etc. So the reason the code got removed was that it was just very grotty and hasn't really been maintained for over a decade. In order to resurrect it we'd not just have to have a maintainer, the whole "it's grotty and incomprehensible and has these nasty interactions with random other things" would need to be addressed too. Linus
