On 13/02/2018 16:44, Michal Hocko wrote: > On Tue 13-02-18 16:03:09, Paolo Bonzini wrote: >> 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). > > We do return NULL for that case regardless the above. The patch just > doesn't warn. Or do you think it is helpful to warn?
It certainly helps bringing potential issues in the spotlight (through fuzzing, mostly). Paolo