On Thu, Mar 02, 2023 at 11:54:03AM -0800, Kees Cook wrote: > On Thu, Mar 02, 2023 at 07:19:49PM +0000, Al Viro wrote: > > On Thu, Mar 02, 2023 at 11:10:03AM -0800, Linus Torvalds wrote: > > > On Thu, Mar 2, 2023 at 11:03 AM Linus Torvalds > > > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > It might be best if we actually exposed it as a SLAB_SKIP_ZERO thing, > > > > just to make it possible to say - exactly in situations like this - > > > > that this particular slab cache has no advantage from pre-zeroing. > > > > > > Actually, maybe it's just as well to keep it per-allocation, and just > > > special-case getname_flags() itself. > > > > > > We could replace the __getname() there with just a > > > > > > kmem_cache_alloc(names_cachep, GFP_KERNEL | __GFP_SKIP_ZERO); > > > > > > we're going to overwrite the beginning of the buffer with the path we > > > copy from user space, and then we'd have to make people comfortable > > > with the fact that even with zero initialization hardening on, the > > > space after the filename wouldn't be initialized... > > > > ACK; same in getname_kernel() and sys_getcwd(), at the very least. > > FWIW, much earlier analysis suggested opting out these kmem caches: > > buffer_head > names_cache > mm_struct > anon_vma > skbuff_head_cache > skbuff_fclone_cache I would probably add dentry_cache to it; the only subtle part is ->d_iname and I'm convinced that explicit "make sure there's a NUL at the very end" is enough.
