On Fri, Aug 20, 2021 at 07:57:25AM -0700, James Bottomley wrote: > On Fri, 2021-08-20 at 06:33 +0200, Jordy Zomer wrote: > > As you can see there's an `atomic_inc` for each `memfd` that is > > opened in the `memfd_secret` syscall. If a local attacker succeeds to > > open 2^32 memfd's, the counter will wrap around to 0. This implies > > that you may hibernate again, even though there are still regions of > > this secret memory, thereby bypassing the security check. > > This isn't a possible attack, is it? secret memory is per process and > each process usually has an open fd limit of 1024. That's not to say > we shouldn't have overflow protection just in case, but I think today > we don't have a problem. But it's a _global_ setting, so it's still possible, though likely impractical today. But refcount_t mitigates it and is a trivial change. :) -- Kees Cook
