Messages in this thread | | | From | Ben Skeggs <> | Date | Wed, 14 Feb 2018 08:57:51 +1000 | Subject | Re: [drm-nouveau-mmu] question about potential NULL pointer dereference |
| |
On Wed, Feb 14, 2018 at 1:40 AM, Gustavo A. R. Silva <garsilva@embeddedor.com> wrote: > > Hi all, > > While doing some static analysis I ran into the following piece of code at > drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c:957: > > 957#define node(root, dir) ((root)->head.dir == &vmm->list) ? NULL : > \ > 958 list_entry((root)->head.dir, struct nvkm_vma, head) > 959 > 960void > 961nvkm_vmm_unmap_region(struct nvkm_vmm *vmm, struct nvkm_vma *vma) > 962{ > 963 struct nvkm_vma *next; > 964 > 965 nvkm_memory_tags_put(vma->memory, vmm->mmu->subdev.device, > &vma->tags); > 966 nvkm_memory_unref(&vma->memory); > 967 > 968 if (vma->part) { > 969 struct nvkm_vma *prev = node(vma, prev); > 970 if (!prev->memory) { > 971 prev->size += vma->size; > 972 rb_erase(&vma->tree, &vmm->root); > 973 list_del(&vma->head); > 974 kfree(vma); > 975 vma = prev; > 976 } > 977 } > 978 > 979 next = node(vma, next); > 980 if (next && next->part) { > 981 if (!next->memory) { > 982 vma->size += next->size; > 983 rb_erase(&next->tree, &vmm->root); > 984 list_del(&next->head); > 985 kfree(next); > 986 } > 987 } > 988} > > The issue here is that in case _node_ returns NULL, _prev_ is not being null > checked, hence there is a potential null pointer dereference at line 970. > > Notice that _next_ is being null checked at line 980, so I wonder if _prev_ > should be checked the same as _next_. > > The fact that both _next_ and next->part are null checked, makes me wonder > if in case _prev_ actually needs to be checked, there is another pointer > contained into _prev_ to be validated as well? I'm sorry, this is not clear > to me at this moment. It's not checked because it can't happen. If vma->part is set, there will be a previous node that it was split from.
Ben.
> > I appreciate your feedback > Thank you > -- > Gustavo > > > > > >
| |