On Sat, Mar 30, 2019 at 10:45 PM Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > > On Thu, Mar 28, 2019 at 4:38 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > > > This nasty little syzbot repro: > > https://syzkaller.appspot.com/x/repro.syz?x=12c7a94f400000 > > > > Creates overlay mounts where the same directory is both in upper > > and lower layers. Simplified example: > > > > mkdir foo work > > mount -t overlay none foo -o"lowerdir=.,upperdir=foo,workdir=work" > > Shouldn't the mount fail in this case? > > Does it make any sense to allow overlapping layers? > > If doing the check the dumb way, the number of d_ancestor() calls > would increase quadratically with the number of layers, but I think > it's possible to do it in linear time if necessary. > Miklos, I saw you did not pick this one for next. IMO, regardless of preventing mount with overlapping layers, the WARN_ON() is inappropriate and this patch that replaces it with pr_warn_reatelimited() has merit on its own. WARN_ON() should reflect a case that we don't think is possible in current code and as API constrain assertion. Neither is the case here. We know that it *is* possible to hit this case, even with checking overlapping layers on mount and user does get an error when we hit the case. Thanks, Amir.
