On Thu, Mar 02, 2023 at 07:14:24PM +0100, Mateusz Guzik wrote: > On 3/2/23, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, Mar 2, 2023 at 12:30 AM Christian Brauner <brauner@xxxxxxxxxx> > > wrote: > >> > >> Fwiw, as long as you, Al, and others are fine with it and I'm aware of > >> it I'm happy to pick up more stuff like this. I've done it before and > >> have worked in this area so I'm happy to help with some of the load. > > > > Yeah, that would work. We've actually had discussions of vfs > > maintenance in general. > > > > In this case it really wasn't an issue, with this being just two > > fairly straightforward patches for code that I was familiar with. > > > > Well on that note I intend to write a patch which would add a flag to > the dentry cache. > > There is this thing named CONFIG_INIT_ON_ALLOC_DEFAULT_ON which is > enabled at least on debian, ubuntu and arch. It results in mandatory > memset on the obj before it gets returned from kmalloc, for hardening > purposes. > > Now the problem is that dentry cache allocates bufs 4096 bytes in > size, so this is an equivalent of a clear_page call and it happens > *every time* there is a path lookup. Huh? Quite a few path lookups don't end up allocating any dentries; what exactly are you talking about? > Given how dentry cache is used, I'm confident there is 0 hardening > benefit for it. > > So the plan would be to add a flag on cache creation to exempt it from > the mandatory memset treatment and use it with dentry. > > I don't have numbers handy but as you can imagine it gave me a nice bump :) > > Whatever you think about the idea aside, the q is: can something like > the above go in without Al approving it? That one I would really like to take a look at.
