On Tue, Jun 02, 2020 at 04:15:17PM +0200, Vlastimil Babka wrote: > SLUB allows runtime changing of page allocation order by writing into the > /sys/kernel/slab/<cache>/order file. Jann has reported [1] that this interface > allows the order to be set too small, leading to crashes. > > While it's possible to fix the immediate issue, closer inspection reveals > potential races. Storing the new order calls calculate_sizes() which > non-atomically updates a lot of kmem_cache fields while the cache is still in > use. Unexpected behavior might occur even if the fields are set to the same > value as they were. > > This could be fixed by splitting out the part of calculate_sizes() that > depends > on forced_order, so that we only update kmem_cache.oo field. This could still > race with init_cache_random_seq(), shuffle_freelist(), allocate_slab(). > Perhaps > it's possible to audit and e.g. add some READ_ONCE/WRITE_ONCE accesses, it > might be easier just to remove the runtime order changes, which is what this > patch does. If there are valid usecases for per-cache order setting, we could > e.g. extend the boot parameters to do that. > > [1] > https://lore.kernel.org/r/cag48ez31pp--h6_fzvyfj4h86qyczafpdxtjhueean+7vje...@mail.gmail.com > > Reported-by: Jann Horn <ja...@google.com> > Signed-off-by: Vlastimil Babka <vba...@suse.cz>
Reviewed-by: Kees Cook <keesc...@chromium.org> -- Kees Cook
