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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>
This commit is contained in:
Daniel De Graaf 2013-01-02 22:57:11 +00:00 committed by Konrad Rzeszutek Wilk
parent 99beae6cb8
commit 2512f298cb
1 changed files with 24 additions and 5 deletions
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29
drivers/xen/gntdev.c
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@ -378,7 +378,20 @@ static void gntdev_vma_close(struct vm_area_struct *vma)
struct grant_map *map = vma->vm_private_data;
pr_debug("gntdev_vma_close %p\n", vma);
map->vma = NULL;
if (use_ptemod) {
struct file *file = vma->vm_file;
struct gntdev_priv *priv = file->private_data;
/* It is possible that an mmu notifier could be running
* concurrently, so take priv->lock to ensure that the vma won't
* vanishing during the unmap_grant_pages call, since we will
* spin here until that completes. Such a concurrent call will
* not do any unmapping, since that has been done prior to
* closing the vma, but it may still iterate the unmap_ops list.
*/
spin_lock(&priv->lock);
map->vma = NULL;
spin_unlock(&priv->lock);
}
vma->vm_private_data = NULL;
gntdev_put_map(map);
}
@ -579,25 +592,31 @@ static long gntdev_ioctl_get_offset_for_vaddr(struct gntdev_priv *priv,
struct ioctl_gntdev_get_offset_for_vaddr op;
struct vm_area_struct *vma;
struct grant_map *map;
int rv = -EINVAL;
if (copy_from_user(&op, u, sizeof(op)) != 0)
return -EFAULT;
pr_debug("priv %p, offset for vaddr %lx\n", priv, (unsigned long)op.vaddr);
down_read(&current->mm->mmap_sem);
vma = find_vma(current->mm, op.vaddr);
if (!vma || vma->vm_ops != &gntdev_vmops)
return -EINVAL;
goto out_unlock;
map = vma->vm_private_data;
if (!map)
return -EINVAL;
goto out_unlock;
op.offset = map->index << PAGE_SHIFT;
op.count = map->count;
rv = 0;
if (copy_to_user(u, &op, sizeof(op)) != 0)
out_unlock:
up_read(&current->mm->mmap_sem);
if (rv == 0 && copy_to_user(u, &op, sizeof(op)) != 0)
return -EFAULT;
return 0;
return rv;
}
static long gntdev_ioctl_notify(struct gntdev_priv *priv, void __user *u)