On 13/02/2018 15:48, Michal Hocko wrote: > On Thu 08-02-18 13:35:08, David Rientjes wrote: >> The KVM_SET_GSI_ROUTING ioctl does a vmalloc() of >> sizeof(struct kvm_irq_routing_entry) multiplied by a user-supplied value. >> This can be up to 4096 entries on architectures such as arm64 and s390 >> (and the upper bound may be increased on s390 eventually). >> >> This can produce a vmalloc allocation failure warning: >> >> vmalloc: allocation failure: 0 bytes, >> mode:0x24000c2(GFP_KERNEL|__GFP_HIGHMEM) > > I am not arguing about the kvm change but do we actaully want to warn > for 0 sized allocations? This just doesn't make much sense to me. > In other words don't we want this? > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 673942094328..c5d832510c54 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -1748,7 +1748,9 @@ void *__vmalloc_node_range(unsigned long size, unsigned > long align, > unsigned long real_size = size; > > size = PAGE_ALIGN(size); > - if (!size || (size >> PAGE_SHIFT) > totalram_pages) > + if (!size) > + return NULL; > + if ((size >> PAGE_SHIFT) > totalram_pages) > goto fail; > > area = __get_vm_area_node(size, align, VM_ALLOC | VM_UNINITIALIZED | >
There have been quite a few reports of this from syzkaller and generally we've fixed them. It does seem like a recipe for NULL-pointer dereferences when the size is user-controlled (as in this case). But here I'm actually not sure that the "allocation failure: 0 bytes" can happen, since we have a check above for "if (routing.nr)", and there is a check also so that the maximum allocation here is a meager 128 KiB. So I'm wondering if this patch is obsolete actually after commit f8c1b85b2523. David? Thanks, Paolo Paolo
