Quoting Ben Skeggs <bske...@redhat.com>:
On Wed, Feb 14, 2018 at 1:40 AM, Gustavo A. R. Silva
<garsi...@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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