Messages in this thread | | | Date | Tue, 13 Feb 2018 17:00:16 -0600 | From | "Gustavo A. R. Silva" <> | Subject | Re: [drm-nouveau-mmu] question about potential NULL pointer dereference |
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Quoting Ben Skeggs <bskeggs@redhat.com>:
> 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. >
I got it.
Thanks, Ben. -- Gustavo
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