Messages in this thread | | | From | Nick Piggin <> | Subject | Re: [RFC] vivi, videobuf_to_vmalloc() and related breakage | Date | Mon, 15 Oct 2007 17:59:19 +1000 |
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On Monday 15 October 2007 12:01, Al Viro wrote: > AFAICS, videobuf-vmalloc use of mem->vma and mem->vmalloc is > bogus. > > You obtain the latter with vmalloc_user(); so far, so good. Then you have > retval=remap_vmalloc_range(vma, mem->vmalloc,0); > where vma is given to you by mmap(); again, fine - we get the memory > pointed to be mem->vmalloc() mapped at vma->vm_start. > > Now we get the trouble: things like > > static void vivi_fillbuff(struct vivi_dev *dev,struct vivi_buffer *buf) > { > ... > void *vbuf=videobuf_to_vmalloc (&buf->vb); > ... > copy_to_user(vbuf + ..., ..., ...) > > get vbuf equal to ->vmalloc of buf->vp.priv and that is _not_ a userland > address. Giving it to copy_to_user() is not going to do anything good. > On some targets it'll fail, on some - write to unrelated user memory. > What is going on there? If that's an attempt to copy into that buffer > allocated by vmalloc_user(), why are we doing copy_to_user() at all?
Right you are. remap_vmalloc_range doesn't turn the passed vmalloc area into user memory (it creates a completely new mapping).
Presumably it either wants to copy_to_user to that new mapping, or memcpy to ->vmalloc? Would the former be an attempt to avoid some virtual aliasing issues?
> But there's more; we have made a copy of vma (kmalloc+memcpy), stored it in > mem->vma and later we cheerfully do remap_vmalloc_range(mem->vma,....). > And kfree that mem->vma immediately afterwards. What the hell? It might > not break now, but that seems to be playing very fast and loose with the > warranties provided by VM.
I don't know why one would be finding remap_vmalloc_range to fail it mmap time but not later? Should just do it at mmap time and if that is failing, then work out why (or ask linux-mm for help). Actually there is probably a window where we can get subsequent anonymous pages faulted into the empty vma there if we haven't remapped it, then the subsequent attempt to remap will hit the BUG_ON in remap_pte_range.
(that's aside from the big conceptual problem with passing in an "invented" vma... don't do that! (: ) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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