Messages in this thread | | | Date | Fri, 21 Dec 2012 15:18:24 -0500 | From | Konrad Rzeszutek Wilk <> | Subject | Re: oopsable race in xen-gntdev (unsafe vma access) |
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On Sat, Dec 15, 2012 at 06:12:11PM +0000, Al Viro wrote: > 1) find_vma() is *not* safe without ->mmap_sem and its result may > very well be freed just as it's returned to caller. IOW, > gntdev_ioctl_get_offset_for_vaddr() is racy and may end up with > dereferencing freed memory. > > 2) gntdev_vma_close() is putting NULL into map->vma with only > ->mmap_sem held by caller. Things like > if (!map->vma) > continue; > if (map->vma->vm_start >= end) > continue; > if (map->vma->vm_end <= start) > done with just priv->lock held are racy. > > I'm not familiar with the code, but it looks like we need to > protect gntdev_vma_close() guts with the same spinlock and probably > hold ->mmap_sem shared around the "find_vma()+get to map->{index,count}" > in the ioctl. Or replace the logics in ioctl with search through the > list of grant_map under the same spinlock... > > Comments? Hey Al,
Thank you for your analysis.
CC-ing Daniel, David and Stefano. I recall we had some priv->lock movement in the past and there is also interaction with another piece of code - the balloon code so we better be circumspect of not blowing up.
Al, it is around holidays and folks are mostly gone - so this will take a bit of time to get sorted out.
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