On Fri, 5 Feb 2016, Dmitry Vyukov wrote: > On Thu, Feb 4, 2016 at 11:11 PM, David Rientjes <rient...@google.com> wrote: > > On Thu, 4 Feb 2016, Dmitry Vyukov wrote: > > > >> Size of kmalloc() in vc_do_resize() is controlled by user. > >> Too large kmalloc() size triggers WARNING message on console. > >> > >> Use __GFP_NOWARN for this kmalloc() to not scare admins. > >> > > > > Hmm, this is hitting the WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN)) for > > order >= MAX_ORDER. > > > > vc_do_resize() has > > > > if (cols > VC_RESIZE_MAXCOL || lines > VC_RESIZE_MAXROW) > > return -EINVAL; > > > > so the appropriate fix would seem to be to reject sizes that would exceed > > the page allocator's ability to return contiguous memory (MAX_ORDER) > > rather than ever trying the allocation in the first place. > > Hi David, > > Please see Alan response to original report here: > https://groups.google.com/d/msg/syzkaller/ufjvr5j0URo/lTlpYP0DBQAJ > I can't say that I fully understand it. >
vc_do_resize() might not know a stricter limit, but we know the limit that the page allocator can provide, and that's MAX_ORDER-1. kmalloc() with a size >= (1 << (PAGE_SHIFT + MAX_ORDER)) will always fail, so if that is really the upper limit, then so be it. We should return -EINVAL appropriately and not -ENOMEM. I'm thinking that the actual limit would actually be (1 << (PAGE_SHIFT + pageblock_order)) since even memory compaction isn't going to be able to defragment more than that, but the absolute max would always be MAX_ORDER-1.
