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 Alexander's analysis more recently[2] of skbuff went a bit further, I think, and allowed opt-out for non-kmem cache page allocations too. -Kees [1] https://lore.kernel.org/all/20190514143537.10435-5-glider@xxxxxxxxxx/ -- Kees Cook
