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. 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? If so, I'll try to find time to hack it up this or next week. I had some other patches to write too, but $reallife. -- Mateusz Guzik <mjguzik gmail.com>
