On Thu, Aug 1, 2024 at 2:54 PM Andrey Konovalov <andreyknvl@xxxxxxxxx> wrote: > On Thu, Aug 1, 2024 at 6:01 AM Jann Horn <jannh@xxxxxxxxxx> wrote: > > > > > > @@ -503,15 +509,22 @@ bool __kasan_mempool_poison_object(void *ptr, unsigned long ip) > > > > kasan_poison(ptr, folio_size(folio), KASAN_PAGE_FREE, false); > > > > return true; > > > > } > > > > > > > > if (is_kfence_address(ptr)) > > > > return false; > > > > + if (!kasan_arch_is_ready()) > > > > + return true; > > > > > > Hm, I think we had a bug here: the function should return true in both > > > cases. This seems reasonable: if KASAN is not checking the object, the > > > caller can do whatever they want with it. > > > > But if the object is a kfence allocation, we maybe do want the caller > > to free it quickly so that kfence can catch potential UAF access? So > > "return false" in that case seems appropriate. > > Return false would mean: allocation is buggy, do not use it and do not > free it (note that the return value meaning here is inverse compared > to the newly added check_slab_allocation()). And this doesn't seem > like something we want for KFENCE-managed objects. But regardless of > the return value here, the callers tend not to free these allocations > to the slab allocator, that's the point of mempools. So KFENCE won't > catch a UAF either way. Oooh, right, I misunderstood the semantics of the function. I'll change it in v6.
