xen/gntdev: fix unsafe vma access
In gntdev_ioctl_get_offset_for_vaddr, we need to hold mmap_sem while calling find_vma() to avoid potentially having the result freed out from under us. Similarly, the MMU notifier functions need to synchronize with gntdev_vma_close to avoid map->vma being freed during their iteration. Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov> Reported-by: Al Viro <viro@ZenIV.linux.org.uk> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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@ -378,7 +378,20 @@ static void gntdev_vma_close(struct vm_area_struct *vma)
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struct grant_map *map = vma->vm_private_data;
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pr_debug("gntdev_vma_close %p\n", vma);
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map->vma = NULL;
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if (use_ptemod) {
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struct file *file = vma->vm_file;
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struct gntdev_priv *priv = file->private_data;
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/* It is possible that an mmu notifier could be running
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* concurrently, so take priv->lock to ensure that the vma won't
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* vanishing during the unmap_grant_pages call, since we will
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* spin here until that completes. Such a concurrent call will
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* not do any unmapping, since that has been done prior to
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* closing the vma, but it may still iterate the unmap_ops list.
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*/
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spin_lock(&priv->lock);
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map->vma = NULL;
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spin_unlock(&priv->lock);
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}
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vma->vm_private_data = NULL;
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gntdev_put_map(map);
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}
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@ -579,25 +592,31 @@ static long gntdev_ioctl_get_offset_for_vaddr(struct gntdev_priv *priv,
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struct ioctl_gntdev_get_offset_for_vaddr op;
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struct vm_area_struct *vma;
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struct grant_map *map;
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int rv = -EINVAL;
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if (copy_from_user(&op, u, sizeof(op)) != 0)
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return -EFAULT;
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pr_debug("priv %p, offset for vaddr %lx\n", priv, (unsigned long)op.vaddr);
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down_read(¤t->mm->mmap_sem);
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vma = find_vma(current->mm, op.vaddr);
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if (!vma || vma->vm_ops != &gntdev_vmops)
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return -EINVAL;
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goto out_unlock;
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map = vma->vm_private_data;
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if (!map)
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return -EINVAL;
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goto out_unlock;
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op.offset = map->index << PAGE_SHIFT;
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op.count = map->count;
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rv = 0;
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if (copy_to_user(u, &op, sizeof(op)) != 0)
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out_unlock:
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up_read(¤t->mm->mmap_sem);
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if (rv == 0 && copy_to_user(u, &op, sizeof(op)) != 0)
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return -EFAULT;
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return 0;
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return rv;
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}
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static long gntdev_ioctl_notify(struct gntdev_priv *priv, void __user *u)
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